What is the proper auxiliary verb in: You _______ to finish your work today.

Answer 1

There are two options:

(1) HAVE: You have to finish your homework today.

(2) OUGHT: You ought to finish your homework today.

If you were wondering why you cannot use 'must' or 'should', the reason is the preposition 'to' that is already given and requires a modal verb that uses 'to'; 'must' and 'should' do not use 'to'.

Answer 2

There are a few options for the auxiliary verb, or helping verb, in this sentence. One of them is need, which makes the sentence, "You need to finish your work today." The other that I'm aware of is have, which makes the sentence, "You have to finish your work today."