381. For starters, cabin pressures at high altitudes are set at roughly what they would be if you lived at 5000 to 8000 feet abase sea level.

英语四级译文:
对于初试者，高空舱内压力被大体设定为相当于居住在海拔5000到8000英尺处所承受的压力。

四级词汇讲解:
what引导的是介词at的宾语从句，what在从句中充当表语。

high altitudes意为“高空，高海拔地区”。如:
This type of breathing is not considered abnormal at high altitudes.这种呼吸在高海拔地区不被看成是不正常的。

sea level意为“海平面”。如:
The top of the hill is just 50 meters above sea level.这座小山的山顶只有海拔50米。

英语四级考点归纳:
有关set的常见短语为:

※ be (all) set for sth./to do sth.意为“准备好(做)某事”。如:
We are all set for victory in the election.我们决意要在选举中获胜。
He was set to go when the bell rang.他准备好要走时，门铃响了。

※ set sth. aside意为“把某事物放在一边;节省或保留出”。如:
He set aside his book and lit a cigarette.他把书放到一边，点了一支烟。
You should set aside a few minutes each day to do some exercises.你应该每天抽出一些时间来锻炼一下身体。

※ set off意为“开始”。如:
We'd better set off for the station immediately.我们最好立刻动身去火车站。