In China it is believed that spring is a season people often feel sleepier.A. thatB. whic

问题补充：

In China, it is believed that spring is a season people often feel sleepier.

A. that

B. which

C. as

D. when

答案：

A. that

B. which

C. as

(答案→)D. when

解析：在中国，大家都相信春天是一个人们会感觉更困的季节。这里使用了定语从句，先行词是a season，定语从句中不缺主宾表，缺少的是时间状语，所以用when引导定语从句，选D。