问题
选择题
Cheer up! Everyone may have periods in their lives everything seems tough．
A．when
B．where
C．which
D．that
答案
答案：A
考查定语从句。定语从句When everything seems tough修饰先行词periods, 本定语从句很完整，且先行词表示时间，所以使用关系副词when.句意：振作起来！在人生中每个人都有什么都不顺利的时期的。