常用的倒凹深度有()
A．0.20mm
B．0.25mm
C．0.50mm
D．0.75mm
E．1.00mm
参考答案：B, C, D
What else do you do winter in China? [ ]
A. on
B. at
C. in
下列代数式表示a、b的平方和的是[ ]
A.（a+b）2
B.a+b2
C.a2+b
D.a2+b2
