在Rt △ABC 中，各边都扩大5 倍，则角A的三角函数值[ ]
A.不变
B.扩大5倍
C.缩小5倍
D.不能确定
A
We were having a meeting ______ suddenly someone knocked at the door. [ ]
A. because
B. when
C. as
D. while
简述假肢安装的理想条件。
