铆钉并列排列铆接时，铆钉间距应（）3倍铆钉直径。
A．小于
B．大于
C．小于或等于
D．大于或等于
参考答案：D
白球比红球少10%，表示______的数量是______的数量的90%．
His sister left home in 1998, and__________ since.
A．had not been heard of
B．has not been heard of
C．had not heard of
D．has not heard of
