WINDOWS2000 SERVER可以做（）。
参考答案：集群
There is a piece of work．It takes Mr．A alone 20 days to finish，and Mr．B 30 alone days to finish．It takes them（ ）days to work together to finish the work．
A．10
B．12
C．15
D．50
可见于神经梅毒的是( )
A．Marcus-Gunn瞳孔B．A-R瞳孔C．Homer瞳孔D．Adie瞳孔E．以上均不对
