Question

Fill an appropriate auxiliary verb in the blank:
I’m sorry I couldn't come yesterday. I _____ work late.
a. Has to
b. Have to
c. Had to
d. Had

Answer 1

Hint: An auxiliary verb is a helping verb. An auxiliary verb is always followed by a main verb such as work, play, run, eat, etc. A helping verb, as the word says, helps to determine the tense of a sentence.

Complete answer:
In the given question, the person is apologizing for not coming yesterday. So if today is the 18th of May, he is talking about not being able to come on the 17th of May. Thus, he is talking about the past, that is yesterday. The reason was that he was working late on 17th May.
Now, let us look at which of the options will help us identify that he was working late.

> If we use option a, the sentence will be: I’m sorry I couldn't come yesterday. I has to work late.
This is sounding absolutely wrong. ‘Has’ is a present tense. We use a present tense to talk about the present. He is talking about the past. So this is a wrong answer.

> Using option b, the sentence will be: I have to work late.
‘Have’ is a future tense. He is not talking about the work he has to do on the 19th of May. He is not talking about the work he has to do in the future. So this option is wrong as well.

> Option c will give us the following sentence: I had to work late.
Now, this sentence makes sense. He is talking about the past since ‘had’ is a past tense. He is telling everyone on 18th May that he had to work late on 17th May which is why he was unable to come. Option c is the correct option.

> If we use option d, we will get the sentence: I had work late.
This is grammatically wrong because we have to use a ‘to’ in the sentence. Thus, this option is also wrong.

Therefore, we can see from the given options and their explanations that option c is the correct answer. Thus, the complete and correct sentence will be: I’m sorry I couldn't come yesterday. I had to work late.

Note: The best way to solve this kind of a question is by using the given options in the given sentence and see if it is making sense. A good grasp over tenses in grammar will help ace these kinds of questions.