各观察值均加(或减)同一个数后()
A.均数不变,标准差改变
B.均数改变,标准差不变
C.两者均改变
D.两者均不变
E.不能确定均数和标准差作何改变
参考答案:B
挤压锚具制作时压力表的油压应符合操作说明书的规定,挤压后预应力筋外端应露出挤压套筒3~8mm。( )
So difficult ___it to work out the problem that I decided to ask Tom for advice.
A.I did find
B.did I find
C.I have found
D.have I found