Each of the students ____ aware of the rules.

Correct answer: 'is'.

Explanation: The word "each" is singular and requires a singular verb. Therefore, the singular present-tense linking verb "is" correctly agrees with the subject in the sentence: "Each of the students is aware of the rules."

• "are" — incorrect because it is a plural verb and does not agree with the singular subject "each."

• "have" — incorrect because it is plural and also does not function as the appropriate linking verb for the adjective "aware."

• "were" — incorrect because it is plural and past tense, so it does not agree with the singular present context required by "each."