根据二次根式的性质，被开方数大于或等于0，
可知：4-x≥0，即x≤4时，二次根式有意义．
故空中填：x≤4．
She ______ for 15 years, yet she didn’t know what kind of man she ______.
A．had married; married
B．had been married; married to
C．had been married; had married
D．married; had married to
《工程网络计划技术规程》推荐的常用工程网络计划类型不包括( )。
A．双代号网络计划
B．单代号网络计划
C．双代号时标网络计划
D．单代号时标网络计划
