2, 3, 4, front. Now we're going to run it off. 2 3 4
前踢。现在, 我们来快跑。
and we have only to turn to that extraordinary discovery of echo-location in bats to see a case in which the voice plays a strictly utilitarian role.
我们只要看一看蝙蝠回声定位这一极不寻常的发现,就可以探究一下声音在什么情况下有绝对的实用价值。