经济困难的

From this a reasoner can deduce that if an individual is a Person, then it is also a Mammal.

一个推理机就可以据此推断：如果某个个体是一个"人"，那么它也是一个"哺乳动物"。

Reverberation describes the reaction of an acoustic environment to sound.

回响描述的是一个声音所处的声学环境的反应。