The correct answer is C. had watched.
The sentence is in the past perfect tense, which is used to talk about an action that happened before another action in the past. In this case, the action that happened before is “read the review,” and the action that happened after is “watch the movie.” Therefore, the correct verb tense is the past perfect, which is formed with the past participle of the verb (“watched”) and the auxiliary verb “had.”
The other options are incorrect because they do not agree with the tense of the sentence. Option A, “watches,” is in the present tense, which is not appropriate for an action that happened before another action in the past. Option B, “have watched,” is in the present perfect tense, which is also not appropriate for an action that happened before another action in the past. Option D, “was watching,” is in the past progressive tense, which is used to talk about an action that was happening at a specific time in the past. In this case, the sentence is not talking about an action that was happening at a specific time in the past, but rather an action that happened before another action in the past. Therefore, the correct verb tense is the past perfect.