在美国，由于“回声潮一代”——即数量突增的年轻人口——起到的促进作用，“多户公寓”租赁业的前景向好。
In America prospects for the "multi-family apartment" rented sector are helped by the "echo-boomers", a youthful bulge in the population.
蝙蝠耳朵的外部结构在接收回声时也起到重要的作用。
The external structure of bats ears also plays an important role in receiving echoes.
动物发出的声音并不是都能当作语言，因此我们只好求助于蝙蝠回声定位的这种非凡的发现，探究一下语音在何种情况下起着绝对有用的作用。
Not all sounds made by animals serve as language, and we have only to turn to that extraordinary discovery of echolocation in bats to see a case in which the voice plays a strictly utilitarian role.
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