题目：
Wind power is an ancient source of energy we may return in the near future.
A．on which
B．by which
C．to which
D．from which
答案：
答案：C
题目分析：句意：风力是古老的能源，我们不久的将来也许会再次回到风力上来。Return to回到，返回；这里which引导的是定语从句，它代替source of energy，故选C。
点评：本题难度适中。定语从句是英语语法中非常重要的内容，在阅读和理解过程中起着极其重要的作用。定语从句的考查关键在于定语从句的成分分析，需要考生有分析理解复杂的句子结构的能力。
即学即练： Tom has made great progress, made us happy.
A. which B. by which C. when D. that
解析：A。句意：汤姆取得了很大的进步，这使我们很高兴。
