The correct answer is A. was cleaning.
The sentence is in the past tense, so the verb must also be in the past tense. Of the four options, only “was cleaning” is in the past tense.
“Is cleaning” is in the present tense, and “cleaned” is in the past participle. “Were cleaning” is the past tense form of the plural verb “to clean.”
Here is a diagram that shows the verb tenses in English:
Tense | Simple | Progressive | Perfect | Perfect Progressive
——- | ——– | ——– | ——– | ——–
Present | I clean | I am cleaning | I have cleaned | I have been cleaning
Past | I cleaned | I was cleaning | I had cleaned | I had been cleaning
Future | I will clean | I will be cleaning | I will have cleaned | I will have been cleaning
I hope this helps!