You know the proverb, Smile and the world smiles with you, cry and you cry alone.
要知道有句格言“微笑,世界与你同欢乐;哭泣,你只能独自悲伤”。
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。