Topic: verb (ক্রিয়া),

Best Answer Explained in Below-:

The question asks which of the provided options can function as both a 'modal verb' and a 'main verb.' In this context, 'need' is the correct answer.

1. **Need as a Modal Verb**: When 'need' acts as a modal verb, it expresses necessity or obligation. For example, in the sentence "You need to finish your homework," 'need' functions to indicate that finishing the homework is essential. In this use, it does not require an auxiliary and directly affects the verb that follows.

2. **Need as a Main Verb**: Conversely, when 'need' is used as a main verb, it conveys a requirement or lack thereof. For instance, in "I need some help," 'need' serves as the primary verb of the sentence. Here, it stands alone and describes the speaker's desire for assistance.

In comparison, the other options do not fulfill both functions. 'Do' primarily functions as an auxiliary or main verb, but not as a modal in a strict sense. 'Could' strictly serves as a modal verb, indicating possibility or ability, without serving as a main verb in standard English. Lastly, 'mind' can function in similar ways but does not fit the modal category. Thus, 'need' stands out as the only option that operates effectively in both capacities.