一个因数的末尾有两个0，另一个因数末尾没有0，积的末尾至少有[ ]
A．2个0
B．3个0
C．1个0
D．2或3个0
答案：A
Jack wasn’t saying anything , but the teacher smiled at him_____he had done something very clever.
A．as if
B．in case
C．while
D．though
用横向磨削法磨削平面时，磨削宽度应等于横向进给量。
