Topic: Conditional Sentence,

Best Answer Explained in Below-:

The sentence "If he runs fast he... win the prize" is a conditional statement that implies a cause-and-effect relationship. In English grammar, the first conditional tense is used to discuss real and possible situations in the future. This structure typically employs "if" followed by a simple present verb, and in the main clause, it uses "will" followed by the base verb.

Option B, "will," fits perfectly in this context: "If he runs fast, he will win the prize." This indicates a strong belief that should the condition of him running fast be met, the outcome of winning the prize is highly likely.

Using "would" (option A) is incorrect because it suggests a hypothetical or less certain situation, more typical of the second conditional which is used for unreal scenarios. "Can" (option C) implies ability and is inappropriate here since we're discussing a future consequence rather than capability. "Could" (option D) suggests possibility but lacks the assertiveness needed for this particular cause-effect relationship. Thus, "will" is the most suitable choice, expressing both certainty and a direct connection between the action and the outcome.