Rahul and his friends . . . . . . . . also invited to the party. A. is B. was C. had D. were

The other options are incorrect because they do not agree with the subject or the time reference. Option A, “is”, is in the present tense, which does not agree with the past tense time reference. Option B, “was”, is in the singular form, which does not agree with the plural subject. Option C, “had”, is in the past participle form, which is not used as the main verb of a sentence.