答案应该是D ==drop out (of -- - -)
其实呢,这四个都是正确的选项.出题人的英语太精深了.他的考点不是语法,而是逻辑.真不知道为什麼这样.As far as I am concerned,such English does much harm to students learning English at your current level.And I strongly suggest that your teacher be talked to about this"bad" English.