(C) have been
The correct answer is have been — "I have been watching that programme every week since it started."
This sentence describes an action that began in the past and continues to the present ("since it started"). This requires the Present Perfect Continuous tense: have/has + been + verb-ing. Since the subject is "I" (first person), we use have been, not "has been" (which is for he/she/it). Option (D) "was been" is grammatically incorrect, and option (B) "had" does not fit the continuous structure required here.