A-A+
We see lightning (before we) hear the thunder
问题详情
We see lightning (before we) hear the thunder (because) sound travels (more slowly) than (light is).
A．before we
B．because
C．more slowly
D．light is
参考答案
正确答案：D
解析：比较级前面是实义动词travel，后面应该用does代替。
