🗣️ 情景例句
He has a big sales office in Los Angeles,
他在Los Angeles有一个大的销售办事处，
I haven't heard from him for a long time.
我很久没有收到他的信了。
a trough (the lowest point), a height (the vertical distance from the trough to the crest),
波谷（最低点）、浪高（从波谷到浪峰的垂直距离）