Explanations:The past continuous tense is used to describe an action that was ongoing at a specific time in the past. It is formed using the auxiliary verb "was" (for singular subjects) or "were" (for plural subjects) followed by the present participle (verb+ing) of the main verb. In this case, the sentence is about Sarala's action of giving tuition when she was in Mumbai, which is a past event. Therefore, the correct tense to use is the past continuous tense.
The sentence structure is as follows: Subject + was/were + verb+ing. Since "Sarala" is a singular subject, we use "was" as the auxiliary verb. The main verb "earn" becomes "earning" in the present participle form. Thus, the correct form is "was earning."
It is important to distinguish between the past continuous tense and the simple past tense. The simple past tense is used to describe a completed action in the past, while the past continuous tense is used to describe an ongoing action in the past. In this context, "was earning" correctly conveys that Sarala was in the process of earning money by giving tuition at a specific time in the past.
Other options like "is earning" and "are earning" are incorrect because they are in the present continuous tense, which describes an action happening now, not in the past. The option "were earning" is incorrect because it is used with plural subjects, and "Sarala" is singular.
Understanding the correct use of verb tenses is crucial for accurate communication in English. The past continuous tense is particularly useful for describing actions that were in progress at a specific time in the past, providing context and background information in narratives.