New Words:

sound [saʊnd]

n. 声音;响声
v. (使)发出声音，响;拉响警报

Sample Sentences：

Could you turn the sound up/down ?
Sound travels more slowly than light.
Sound travels better in water than in air.

travel [ˈtrævl] 长途行走;旅行;转送，传播;

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