Choice (A) fails use to use correct English idiom, because the verb "await" is never followed by a word like "for." You can wait for something or await something, but not "await for." We can eliminate choice (A)--and choice (E), on the same grounds.
Choice (B) has an ungrammatical construction, because the main clause has two grammatical subjects, "students" and "they." The pronoun "they" is grammatically redundant and should be removed from the sentence. We can eliminate choice (B).
Choice (C) is clear and correct. Since the first clause is begun by the subordinating conjunction "because," it's not an independent clause, and therefore it's both correct and required that there is no conjunction before the main clause (which starts with "the students"). Furthermore, the word "because" correctly indicates the cause-and-effect meaning of the sentence.
In choice (D), the phrase "Uncertainty . . . stopped the students to await" doesn't make sense. They students stopped themselves. Furthermore, the phrasing obscures the cause-and-effect meaning of the sentence. We can eliminate choice (D).
The correct answer is (C).