An action in a sentence can be represented in two ways, namely active and passive voice.
The passive voice always uses the past participle form of the main verb irrespective of any tense. Only the auxiliary verbs depend upon the sentence given in the active voice.
The option C is correct as the given sentence is in the active voice and to transform it into passive voice the subject of the given sentence
(the noise) comes in the place of the object (you) and vice-versa.
Also, as the given sentence is interrogative and is in the simple past tense, 'Were you' is used before the object of the given sentence(you)followed by the past participle form of the main verb (frighten).
Options A, B, and D are wrong as the subject as the question must start with 'were', 'were you' cannot be used in the starting of the question as the subject must be 'you' in the transformed sentence, and the past participle of the main verb is not used respectively.
The correct answer is C)Were you frightened by the noise?