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.

英語四級譯文:
對于初試者，高空艙內壓力被大體設定為相當于居住在海拔5000到8000英尺處所承受的壓力。

四級詞匯講解:
what引導的是介詞at的賓語從句，what在從句中充當表語。

high altitudes意為“高空，高海拔地區”。如:
This type of breathing is not considered abnormal at high altitudes.這種呼吸在高海拔地區不被看成是不正常的。

sea level意為“海平面”。如:
The top of the hill is just 50 meters above sea level.這座小山的山頂只有海拔50米。

英語四級考點歸納:
有關set的常見短語為:

※ be (all) set for sth./to do sth.意為“準備好(做)某事”。如:
We are all set for victory in the election.我們決意要在選舉中獲勝。
He was set to go when the bell rang.他準備好要走時，門鈴響了。

※ set sth. aside意為“把某事物放在一邊;節省或保留出”。如:
He set aside his book and lit a cigarette.他把書放到一邊，點了一支煙。
You should set aside a few minutes each day to do some exercises.你應該每天抽出一些時間來鍛煉一下身體。

※ set off意為“開始”。如:
We'd better set off for the station immediately.我們最好立刻動身去火車站。