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 active voice.
The correct answer is C)We are being followed (by someone).
The option C is correct as the given sentence is in active voice and to transform it into passive voice , the object of the given sentence (us) comes in the place of the subject(somebody) and vice versa. Also, as the sentence is in the present continuous tense, 'being' is added after the helping verb 'are' and before the past participle form of the main verb(follow).
Options A,B, and D are wrong as being is missing , were , and were being cannot be used respectively.