C is correct

1st split: "opportunity to" vs "opportunity of"

Idiomatically, "opportunity of" is incorrect; eliminate all answers that use this construct. Eliminate D and E

2nd split: "be given" vs "should be given" vs "are given" vs "will be given"

The verb mandates and other verbs that express hope, command or request trigger the subjunctive because the action they express may or may not actually happen. When using these verbs, the verb that expresses the action must be in the infinitive form (without to)

Her father asked that she takes her exams. Incorrect.
Her father asked that she take her exams. Correct.
The computer requested that he should enter a password. Incorrect.
The computer requested that he enter a password. Correct
The act mandates that students are given opportunity. Incorrect
The act mandates that students be given opportunity. Correct

The act mandates that students give opportunity. Grammatically correct, but wrong meaning.

Elminate answers that fail to use the subjunctive. Eliminate A, B, and D.

The only remaining answer is C. C, I think, is the correct answer.

(I study with OG and GMATFix Verbal Flashcards)

IMO C, I agree with Ted.

Andrew

Good explanation Ted, OA is C

With verbs indicating command (like mandate here) you need the subjunctive.