Choose the correct passive form from the options given below:
A cardigan ___________ by the old lady at that time.
An action in a sentence can be represented in two ways, namely active and passive voice.
The passive voice always uses the past participle form of the main verb irrespective of any tense. Only the auxiliary verbs depend upon the sentence given in active voice.
The given sentence is in the active voice.
The correct answer is C) Was being knitted
Option C) is correct as 'at that time refers past continuous tense.
Options A, B, and D are not correct as 'was' alone and 'has' cannot be used, and 'knit' is not used in its third form.