Complete the answer to the question with the correct form of ‘able to’:
A: Did you finish your work this afternoon?
B: Yes, there was nobody to disturb me, so I ____________ finish it.
A) Am able to
B) Is able to
C) Was able to
D) Were able to

Hint: Past tense is used to refer to an action or event in the past or an event that has happened in the past. For example: It rained yesterday.

Complete answer:
Option A) Am able to – is an incorrect answer because the conversation between A and B are in past tense. And ‘am able to’ is in the simple present tense and the use of this option in the blank is grammatically incorrect. Thus, this is an incorrect answer.
Option B) Is able to – is an incorrect answer because the meaning of ‘is able to’ is ‘having the power, skill, means, or opportunity to do something’ and this is not in past tense but in present tense. Thus, this is an incorrect answer.
Option C) Was able to – is the correct answer because ‘was able to’ means ‘that he was successfully able to finish his homework as there was nobody there to disturb him. So, the use of ‘was able to’ in the sentence is grammatically correct and we use ‘was’ is an auxiliary verb of am, is and are. And was is used for singular objects. Thus, this is the correct answer.
Option D) Were able to – is an incorrect answer because ‘were’ is second person singular past, and were is also used for the plural objects and here there is nothing plural there in the sentence. Thus, this is an incorrect answer.
A: Did you finish your work this afternoon?
B: Yes, there was nobody to disturb me, so I was able to finish it. (Option C)

Hence, the correct answer is option ‘C’.

Note:There is a major difference between was and were and the difference is that ‘was and were’ are the past tense form of the auxiliary verb am, is and are. ‘Was’ used for the singular objects and ‘were’ is used for the plural objects. So, Option C is the most appropriate answer as compared to any other option because here singular object is used instead of plural.