Select an acceptable pronoun to complete this sentence. Each of the boys tried square best to win the medal.

The correct pronoun to complete the sentence is "his." The sentence should read: "Each of the boys tried his best to win the medal."Explanation: The word "each" is a singular pronoun, so it requires a singular pronoun to match. In this context, "his" is used as the singular possessive pronoun that corresponds with "each of the boys."