Question

Fill in the blank with a suitable modal:
Good morning sir, what _______ I do for you?
A. Would
B. Can
C. Shall
D. Must

Answer 1

Hint:A Modal verb is a type of verb used to denote modality, i.e. possibility, ability, permission, request, ability, suggestions, order, duty, or advice. The base form of another verb that has semantic content is often followed by modal verbs.

Complete answer:
To express capability and also to make a friendly request, CAN is used.
In the sentence given, the speaker asks what he can do for him.Thus, the correct answer is 'Can'
The choices remaining are incorrect because:
The past tense of would is Will.
The future tense is expressed by SHALL.
'MUST' expresses compulsion.

Additional Information:
Modals are special verbs that behave irregularly in English (also called modal verbs, modal auxiliary verbs, modal auxiliaries). They vary from standard verbs such as "job, play, visit ..." They provide additional details about the main verb 's function that follows it. They have a wide range of communicative positions.
Here are some features that modal verbs have:
1. They never alter their shape. You would not be able to add "s", "ed", "ing" ...
2. They are often preceded without "to" by an infinitive (i.e. the bare infinitive.)
3. They are used to indicate modality that allows speakers to express certainty, choice, willingness, duty, need, capacity.

Hence the correct answer is option ‘B’

Note: To answer this type of question you need to develop the basic understanding about the common modal verbs. Here is a list of modal verbs:

Can, could, may, might, will, would, shall, should, must
The verbs or expressions dare, ought to, had better, and need not behave like modal auxiliaries to a large extent and may be added to the above list.