Shell功能包括（）。
A.变量的值的替换
B.命令的替换
C.自动补齐
D.I/O重定向和管道
参考答案：A, B, C, D
口腔颌面部间隙感染脓肿切开引流术的目的是消除病因，使病变彻底治愈。
People taking the therapy learn what scientists _____ for years-laughter is the best medicine. [ ]
A. know
B. knew
C. have known
D. had known
