BREB Assistant Enforcement Coordinator Exam: 2021প্রশ্ন ও সমাধান

Correct answer: (c) @

The Internet Message Format standard (RFC 5322) defines an e-mail address (addr-spec) as local-part "@" domain. The "@" (at sign) is therefore compulsory: it separates the mailbox name from the domain that receives the mail, as in user@example.com. An address without "@" is not a valid e-mail address.

Why the other options are wrong

• (a) $: The dollar sign is allowed in the local part, but it is optional; most addresses never use it.
• (b) N: Letters are allowed, but no particular letter is required in an address.
• (d) &: Like "$", the ampersand is a permitted but optional character in the local part.

Tip: Every e-mail address = username + @ + domain; "@" is the only symbol that must always appear.

Source: RFC 5322: Internet Message Format, §3.4.1 Addr-Spec Specification — RFC Editor

Correct answer: (a) Operating System

Linux is a free, open-source, Unix-like operating system, started by Linus Torvalds in 1991 and released under the GNU GPL. Strictly, "Linux" is the kernel: the core that manages the CPU, memory, devices and processes. A distribution such as Ubuntu, Fedora or Debian bundles that kernel with system tools and applications into a complete OS. In both senses Linux is system software that sits between the hardware and the programs users run.

Why the other options are wrong

• (b) Application Program: an application performs a user task (word processing, browsing) on top of an OS; Linux is the OS those programs run on.
• (c) Antivirus software: antivirus is a security utility that runs on an OS; Linux itself is not one.
• (d) Firewall: a firewall filters network traffic. The Linux kernel has packet-filtering features, but Linux as a whole is an operating system, not a firewall product.

Tip: Windows, macOS, Linux, UNIX, Android and iOS are all operating systems.

Sources: Linux kernel release README: What is Linux? — kernel.org; Operating System — NIST glossary

Correct answer: (c) Monitor

An output device carries the results of processing from the computer to the user. A monitor turns the computer's video signal into text and images on a screen, so it is a classic output device, along with printers and speakers.

Why the other options are wrong

• (a) Microphone: an input device; it turns sound into a signal that goes into the computer.
• (b) CD-Drive: a secondary storage device. It reads data from a disc (and a writer can record to one); it is grouped with storage, not with output devices like the monitor.
• (d) None of them: wrong, because the monitor is an output device.

Tip: Input = data into the computer (keyboard, mouse, microphone, scanner). Output = results out to the user (monitor, printer, speaker).

Source: Parts of a computer system (Longwood University, CMSC 121)

Correct answer: (c) Input device

Data enter a computer through input devices, which convert information from the outside world into signals the computer can process. Examples are the keyboard, mouse, touchpad, scanner, microphone and sensors.

Why the other options are wrong

• (a) Software: programs process data inside the computer; they are not the physical path by which data come in.
• (b) Output device: works in the opposite direction, presenting results to the user (monitor, printer, speaker).
• (d) Memory: holds data and programs after they have been entered; it is not the entry point from the user.

Tip: Input → Process → Output, with storage holding data in between.

Source: Parts of a computer system (Longwood University, CMSC 121)

Correct answer: (b) DC

Electricity made directly from sunlight comes from photovoltaic (PV) solar cells. Photons free electrons in the semiconductor (usually silicon), and the built-in field of the p–n junction pushes them in one direction only, so the output is direct current (DC). To run AC appliances or feed the AC grid, a solar system adds an inverter that converts this DC into AC.

Why the other options are wrong

• (a) AC: A PV cell has no rotating machine or alternating field; AC appears only after the inverter.
• (c) Both AC and DC: The cell itself produces only DC; any AC in a solar system is made by the inverter, not by the sunlight conversion.
• (d) None: Wrong, because solar cells clearly produce electricity, and it is DC.

Tip: Solar panel and battery → DC; inverter → AC. (A solar-thermal power plant, which uses sunlight to raise steam for a turbine-driven alternator, gives AC, but exam questions like this mean solar panels.)

Source: How do solar PV panels work? — Lafayette College

Correct answer: (a) step down voltage

A distribution sub-station is where power leaves the high-voltage network and enters the local distribution system. Its transformer takes the incoming transmission or sub-transmission voltage and steps it down to the primary distribution level, which then fans out on feeders to the consumers. In Bangladesh this is typically 33 kV → 11 kV at a 33/11 kV sub-station; pole-mounted transformers then reduce 11 kV to 0.4 kV (400/230 V) for consumers.

Why the other options are wrong

• (b) step up voltage: Voltage is stepped up at the generating station's step-up sub-station, so that power can travel long distances with low current and low losses.
• (c) increase power: A transformer cannot increase power; output power equals input power minus losses.
• (d) increase energy: No sub-station creates energy; energy is only converted and transferred, with some losses.

Tip: Generating station → step-up; transmission → grid; distribution sub-station → step-down.

Source: Introduction to Distribution Systems (EE455) — Iowa State University

Correct answer: (d) A.A'=1

A·A′ = 1 is false. A variable ANDed with its own complement is always 0, because one of the two is always 0: A = 0 gives 0·1 = 0, and A = 1 gives 1·0 = 0. The correct complement law is A·A′ = 0.

Why the other options are wrong
These three are true identities, so they are not the answer to "which is not correct".

• (a) A+0=A: Identity law for OR: 0 + 0 = 0 and 1 + 0 = 1.
• (b) A.1=A: Identity law for AND: 0·1 = 0 and 1·1 = 1.
• (c) A+A'=1: Complement law for OR: one of A and A′ is always 1, so the OR is 1.

Tip: Complement laws come in a pair: A + A′ = 1 and A·A′ = 0.

Source: University of Washington CSE 311: Boolean Algebra Reference Sheet

Correct answer: (b) 80%

The Bangladesh Rural Electrification Board (BREB), through its 80 Palli Bidyut Samities, is the country's largest distribution utility. Its share of all electricity consumers at the time of the paper:

• BREB consumers (May 2021): 3,16,40,131 ≈ 3.164 crore
• National consumers (Power Division, July 2021): ≈ 4.01 crore
• Share = 3.164 ÷ 4.01 × 100% ≈ 78.9% ≈ 80%

Why the other options are wrong

• (a) 70%: Too low; BREB's share was close to 79%.
• (c) 85%: Higher than the actual share.
• (d) 90%: Far higher; DPDC, DESCO, BPDB, NESCO and WZPDCL together serve about a fifth of all consumers.

Exam note: The paper expected 80%, which matched BREB's share (about 79%) in 2021. As of October 2026, BREB reports 3,80,57,631 consumers (April 2026) against 5,03,71,883 national consumers (August 2026): 3.806 ÷ 5.037 × 100% ≈ 75.6%. Today the share is about 76%, so "80%" is an overstatement, though it is still the nearest of these four options. If the question reappears unchanged, choose (b). (BREB's own history page also says it serves about 80% of the rural areas, a separate area figure.)

Source: এক নজরে বাপবিবোর্ড (BREB at a glance, May 2021, archived) — reb.gov.bd; এক নজরে (Power sector at a glance, July 2021, archived) — powerdivision.gov.bd; এক নজরে বাপবিবোর্ড এর কার্যক্রম (April 2026) — reb.gov.bd; এক নজরে বিদ্যুৎ খাত (September 2026) — powerdivision.gov.bd