Is it true? There are two correct answers. The last choice "studied, would pass" is equally correct. Both #2 and #4 are correct uses of Past Subjunctive Mood. Past Subjunctive looks superficially like the ordinary past tense (or past perfect) for all verbs (except for "to be"). "Had" and "studied" are both simple past tense, and hence have the potential to be interpreted as Past Subjunctive. One might be tempted to argue that #2 is a better choice since "had studied" seems to refer more explicity to the past ("last semester"). The truth is quite the opposite. #2 refers more explicitly to the present, not the past. #2 looks like Past Perfect but is not really Past Perfect because "had" is not really Past. "Had" is Past Subjunctive, which is a bit different. #2 is the (hypothetical) Subjunctive equivalent of "If he has studied, he would (or 'will') pass" which talks about the present, not the past. Likewise, #2 talks about the present. #2 means: "If he were, right now at this moment, a student who had studied, then he would have passed."