The day will come _______ coal and oil will be used as raw mater

The day will come _______ coal and oil will be used as raw materials.
A、when
B、whether
C、while
D、as
【正确答案】：A
【题目解析】：译文：煤炭和石油作为原料使用的那一天终会来到。本题考查定语从句。when引导定语从句，修饰先行词day。这句话的谓语部分太短，为了避免头重脚轻，所以将定语从句后置。答案为A。