Each button, when , provides a piece of beautiful music.
A. clicked
B. having clicked
C. clicking
D. being clicked
网友回答
A. clicked
B. having clicked
C. clicking
D. being clicked
解析：句意：每个按钮当被点击的时候，都会有一首优美的音乐。这里使用了状语从句的省略，完整的句子是when each button is clicked，it provides a piece of beautiful music.当主从句的主语一致的时候，可以省略从句的主语和be动词，所以选A。