We are given had saw, has seen, seen, and saw. We are looking for TENSE the SAME of saw or seen in context. Saw is PAST TENSE of see and usually comes after NOUNS and PRONOUNS. Saw is a stand-alone verb. Seen is PAST PARTICIPLE of see usually with have, has, had, was, or were to make a COMPOUND VERB. You can usually pick up the error in usage by just hearing it.
Answer A – No change. ELIMINATE A because saw should be stand-alone and does not need had.
Answer B KEEP B because had seen is the proper form of this past tense with seen with the helping verb had.
Answer C ELIMINATE C because seen must have a helping verb such as had for proper usage.
Answer D ELIMINATE D because it doesn’t sound right.
The Correct Answer is