If he works hard he . . . . . . . . pass.

Answer: Option A

Above incomplete sentence is in mood of Conditional Sentence. After filling up the gap the sentence has turned into an example of Probable Conditional Sentence.
Probable Conditional Sentence means it can happen in reality. Here 'pass' will happen if hard work is done by him.
In Probable Conditional Sentence 'if clause' is written in Simpler Present Tense and next part of the sentence is written in Simple Future Tense. 'If he works hard' is written in Present Indefinite Tense and 'he will pass' is written in Future Indefinite Tense.