Select a suitable verb to complete the sentence.
I was really astonished. I didn’t know what to ____.
(a) Do
(b) Go
(c) Use
(d) Say

Hint: Try to point out the verb and the form it has been used in the given sentence. Find out the tense of the already given verbs and choose the option which agrees with the verb forms.

Complete answer:
 We use singular verbs with singular first-person pronouns. Also, we can comprehend that the person in the sentence is surprised by the action and was unable to do or say anything.
In the given question- We can conclude that X was really astonished. Hence, X didn’t know what to do or say. Here, we have used the plural forms of the verb ‘do’ and ‘say’ because we generally use the plural forms with the pronoun ‘I’.
Now, let’s examine the given options-
Option a- ‘Do’ is a plural verb that indicates the action of performing something. ‘Do’ can be used with the given context because X was really shocked and couldn’t decide what to do. Hence, it is the correct option.
Option b- ‘Go’ is a plural verb that indicates the action of proceeding somewhere. ‘Go’ cannot be used with the given context because it is different in sense. Hence, it is an incorrect option.
Option c- ‘Use’ is a plural verb that indicates the action of operating something. ‘Use’ cannot be used with the given context. Hence, it is an incorrect option.
Option d- ‘Say’ is a plural verb that indicates the action of speaking something. ‘Say’ can be used with the given context because X was really shocked and out of words. Hence, it is the correct option. The correct answer is Option ‘a’ and ‘d’.

Note:
 Keep in mind, we generally use the plural verb forms with the first-person singular pronoun ‘I’. For example- I have, I do, I dance, etc.