六番。大学で、男の学生と女の学生がテストの勉強について話しています。女の学生は、昨日何時間勉強しましたか。

The correct choice is Option 3: '3 hours.' The female student states her study time clearly: 'いつもは1時間しか勉強しないんだけど、昨日は3時間もやったんだ' (Usually I only study for 1 hour, but yesterday I did it for 3 hours). The male student mentions his own time ('2時間') as a distractor. The question is about the female student's study time yesterday. Therefore, 3 hours is correct.