单选题 Passengers may retrieve their items from the overhead locker ______ the safety belt sign has been switched off.
  • (A) meanwhile
  • (B) under
  • (C) although
  • (D) once


【正确答案】 D
【答案解析】[语法] 条件连词once(一旦……)
[错误答案] (A)因为meanwhile(其间)是副词，所以不可以放到连词的位置上。