Thereafter, Jack completely lost interest in the class, but couldn't drop it because it was required. So he chose to "informally" drop it-he goes to class as required, but acts invisible, not asking any questions and avoiding any conversation with the teacher.
至此，蔣家慕對於這門課興趣全失，但因為是必修課又不能退選，於是他採取了自稱為「非正式退選」的策略──還是繼續照常到課，但當自己是隱形人，上課不再發問，也不再與老師有任何對話。