Complete the sentence using don’t/doesn’t/didn’t + have to + appropriate form of given verb:
I’m not particularly busy. I’ve got a few things to do, but I _____ (do) them now.
a. didn’t have to do
b. don’t have to do
c. doesn’t have to be doing
d. doesn’t have to be

Hint: The given sentence already tells us the situation. Look for pointers suggesting which tense to use. The required modal auxiliary is already given in the question.

Complete answer: Verbs are action words that show action (sing),
occurrence (develop), or state of being (exist), usually of a noun. Every sentence requires a verb. The basic form of a verb is known as an infinitive.

In the given sentence, the only catch is the tense of the two verbs. We already have all the necessary information, as it is mentioned in the given question. Now, let us have a look at the first part of the sentence. The subject is ‘I’ and the verb that accompanies it is ‘am’. The verb ‘am’ tells us that the tense required is simple present tense. Then, the second verb required after ‘have to’ will be the bare infinitive.

Now, we know what we are looking for. Let’s look at the given options:
a. didn’t have to do - The verb in this option is not in the simple present tense, so this does not fit into the given sentence. This is not the required answer. So, this is an incorrect option.
b. don’t have to do - The verb in this option is in the simple present tense and it matches the subject of the sentence. This fits perfectly into the given sentence. This is the required answer. So, this is the correct option.
c. doesn’t have to be doing - The verb in this option is in the simple present tense, however, it does not match the subject in the sentence and there is no bare infinitive used. This does not fit into the given sentence. This is not the required answer. So, this is an incorrect option.
d. doesn’t have to be - The verb in this option is in the simple present tense, however, it does not match the subject in the sentence and the incorrect bare infinitive is used. This does not fit into the given sentence. This is not the required answer. So, this is an incorrect option.

Note: we add don't between the subject and the verb. We use Don't when the subject is I, you, we or they. When the subject is he, she or it, we add doesn't between the subject and the verb to make a negative sentence.