Institution: জাতীয় কবি কাজী নজরুল ইসলাম বিশ্ববিদ্যালয় (JKKNIU) Exam: গ ইউনিট || জাতীয় কবি কাজী নজরুল ইসলাম বিশ্ববিদ্যালয় || 2013
Topic: Right Form of Verb, Subject: English Grammar (ইংরেজি গ্রামার)

Best Answer Explained in Below-:

The sentence "If my brother were there he......... what to do" employs a conditional structure, specifically the subjunctive mood, which is used to express hypothetical or contrary-to-fact situations. In this case, the phrase "If my brother were there" indicates a situation that is not real; perhaps the brother is not actually present.

When forming conditional sentences like this, the structure typically utilizes "would" in the main clause to show the consequence of the hypothetical condition. The correct answer, "would know," fits perfectly into this structure: "If my brother were there, he would know what to do." This indicates that the speaker believes that, had the brother been present, he would possess the knowledge required to respond appropriately to the situation.

In contrast, the other options do not fit the grammatical requirements for this type of conditional sentence:

- A) "has known" suggests a completed action not relevant to the present hypothetical.
- B) "will know" implies certainty in the future, which doesn't align with the hypothetical context.
- D) "know" lacks the necessary modal auxiliary "would" to indicate a dependence on the condition.

Thus, "would know" is the correct choice, accurately conveying the intended meaning in a hypothetical scenario.