Explanation: The past continuous tense is used to describe an action that was ongoing at a specific point in the past. It is formed using the auxiliary verb "was" (for singular subjects) or "were" (for plural subjects) followed by the present participle of the main verb (verb+ing). In the given sentence, "Sarala was earning money by giving tuition when she was in Mumbai," the action of earning money was ongoing in the past, and the subject "Sarala" is singular, so the correct form is "was earning."
The sentence provides a context where Sarala was engaged in the activity of giving tuition, which was an ongoing action in the past. The use of "was earning" correctly indicates that this action was happening continuously at a specific time in the past, which is when Sarala was in Mumbai.
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 for ongoing actions. For example, "Sarala earned money" (simple past) would indicate a completed action, whereas "Sarala was earning money" (past continuous) indicates an ongoing action.
In this context, the use of "was earning" is appropriate because it conveys the ongoing nature of the action in the past. The other options are incorrect because they either use the present continuous tense ("is earning" and "are earning"), which describes ongoing actions in the present, or they use the wrong form of the auxiliary verb ("were earning" for a singular subject).
Understanding the past continuous tense is crucial for describing ongoing actions in the past, and it is a common topic in various competitive examinations such as UPSC, SSC, Bank PO, and CLAT. The correct use of verb forms and tenses is essential for clear and accurate communication in both written and spoken English.