命令别名是在命令行中代替整个命令名而输入的缩写，用户自定义的命令别名保存在（）。
参考答案：acad.pgp文件中
Professor Smith, along with his assistants, on the project day and night to meet the deadline
(截止日期). [ ]
A. work
B. working
C. is working
D. were keeping
读下面的“三圈环流简图”，图中数码表示的内容正确的是（）
A.①是极地高气压带
B.②是副极地低气压带
C.③是盛行西风带
D.④为信风带
