语法与词汇 These are students who, at some stage of their undergraduate careers, leave class, either ______, or because they are asked to do so.

【正确答案】 A

【答案解析】本题考查副词的含义。A自愿地；B有选择地；C强制地；D必要地。该句的大意为：在大学学习生涯的某一阶段，一些学生或因为自愿或迫于要求而离开课堂。