Combined Bank Maintenance Engineer MCQ Test: 2018প্রশ্ন ও সমাধান

Correct answer: (c) Application layer

Strictly, e-mail is a service rather than a single protocol; the protocols that carry it are SMTP (sending and relaying), POP3 and IMAP (retrieving). All of them are application-layer protocols: they define the commands and messages that mail programs exchange, and they hand their data to the transport layer (TCP) below them. In both the OSI and TCP/IP models, user-facing services such as e-mail, web (HTTP), file transfer (FTP) and DNS sit in the Application layer.

Why the other options are wrong

• (a) Physical layer: Deals only with sending raw bits as electrical, optical or radio signals over the medium.
• (b) Data Link Layer: Frames data and uses MAC addresses for delivery between neighbouring nodes on one link (e.g. Ethernet); it knows nothing about mailboxes or messages.
• (d) TCP layer: Not a formal layer name; TCP belongs to the Transport layer, which carries the mail protocols' data reliably but does not define e-mail itself.

Tip: If a protocol is named after a user service (mail, web, file transfer, names), it is an Application-layer protocol.

Source: RFC 1123: Requirements for Internet Hosts - Application and Support

Correct answer: (c) stack

Push (add an item at the top) and pop (remove the item at the top) are the basic operations that define a stack, the LIFO structure. Both act on the same end, so the last item pushed is the first one popped.

Why the other options are wrong

• (a) Array: An array is accessed by index (read or write A[i]). Push/pop are not its defining operations. An array can store a stack, but the terms still belong to the stack.
• (b) list: A general list supports insertion and deletion at any position. Some libraries name list methods push/pop, but only so the list can be used as a stack.
• (d) all of these: The terms belong to only one structure, the stack. A queue, for comparison, uses enqueue/dequeue.

Tip: Push/pop means stack (LIFO). Enqueue/dequeue means queue (FIFO).

Source: stack — Dictionary of Algorithms and Data Structures (NIST)

Correct answer: (b) B+ tree

A B+ tree is a balanced, multi-way search tree. Each node holds as many keys as fit in one disk page, so the tree stays only a few levels deep, and every lookup reads one node per level. Internal nodes only route the search; the leaves hold the index entries in sorted order and are linked to each other, so both equality searches and range scans (BETWEEN, >, <) are fast. That is why relational DBMSs build their ordinary indexes on the B-tree family.

Depth for 1,000,000 keys:

• B+ tree with fan-out 100: 100³ = 1,000,000 → about 3 levels → about 3 page reads per lookup.
• Balanced binary tree: 2²⁰ ≈ 1,048,576 → about 20 levels → up to 20 page reads.

Run in SQLite on a 200,000-row table, WHERE email = … was a full SCAN emp; after CREATE INDEX ix_email ON emp(email) the plan became SEARCH emp USING COVERING INDEX ix_email.

Why the other options are wrong

• (a) Binary tree: Each node has at most 2 children, so the tree is far deeper (about log₂ n levels) and, if unbalanced, can degrade into a chain. A B-tree node has many children, which is exactly what makes it suitable for disk.
• (c) Stack: LIFO; only the top element is reachable, so it cannot search by key.
• (d) Linked List: Searching means walking node by node, O(n), with no way to jump to a key.

Tip: Disk-based index → B+ tree (few levels, linked leaves for range queries).

Sources: B+ Trees - CS165 lecture slides, Colorado State University; MySQL 8.0 Reference Manual - Glossary (B-tree)

Correct answer: (c) both A and B

JavaScript goes into a page through the <script> element, and the HTML standard allows <script> both where metadata content is expected (inside <head>) and where phrasing content is expected (practically anywhere inside <body>). The script can be written inline or loaded from a file with <script src="app.js"></script>, in either place.

Why the other options are wrong

• (a) <head>: allowed, but not the only place; scripts in <body> are equally valid.
• (b) <body>: allowed, but not the only place; scripts in <head> are equally valid.
• (d) none: wrong, because both locations are permitted.

Tip: <script> works in both <head> and <body>; put it at the end of <body>, or use defer in <head>, so it does not block the page from rendering.

Sources: HTML Standard: 4.12.1 The script element; <script>: The Script element - MDN Web Docs

Correct answer: (d) None

In Java an object is created with the new operator, for example Box b = new Box();. new allocates memory for the object, runs the constructor named after it, and returns a reference to the new object. Since new is not among options (a) to (c), the answer is (d).

Why the other options are wrong

• (a) class: A keyword used to declare (define) a class, not to create an instance of it.
• (b) scanf: A C library input function; it does not exist in Java (Java reads input with classes such as Scanner).
• (c) print: A method of System.out that writes text to the console; it creates nothing.

Tip: Object creation in Java = new + a constructor call, e.g. new ClassName().

Source: Creating Objects (The Java Tutorials)