Step 1: Subject Analysis. The subject is "He, as well as his friends." This is a compound subject where "as well as" acts as a prepositional phrase and does not alter the singular number of the true subject, "He." Consequently, the verb must agree with the singular subject.
Step 2: Option Analysis. - (A) aren't: Plural verb form. Incorrect for a singular subject. - (B) were: Plural past tense verb. Incorrect for a singular subject. - (C) was: Singular past tense verb. Correctly agrees with the singular subject "He." - (D) has: Present tense verb. Does not align with a past action. Incorrect.
Step 3: Conclusion. The correct option is (C) was, due to subject-verb agreement with the singular subject "He."