Question

【题目】Perhaps the day will come ____ people will be able to breathe clean air in cities．
A.when
B.while
C.as
D.since

Answer 1

【答案】A
【解析】这道题考查定语从句的用法：when引导定语从句修饰the day，因为在定语从句中缺少时间状语，所以用when。句意是：可能人们在城市里能呼吸新鲜空气的日子就快到了。