【题目】The most pleasant thing of the rainy season is _____ one can be entirely free from dust.
A.what
B.that
C.whether
D.why

【答案】B
【解析】题目考查表语从句。句意：雨季最令人愉悦的就是人们可以完全不再受到沙尘暴的困扰。is后跟从句作表语，即表语从句，表语从句不缺少主语、谓语和宾语，因此用that，只起引导作用，故选B。