下列字母中全是轴对称图形的是（ ） A．C、X、D、A、I、N B．U、X、O、C、

压力对柴油加氢精制有什么影响？

We should _______ to take time to do other things. [ ]

A. allow

B. allowed

C. be allow

D. be allowed

Jane warns us that our group is going to be very tired and dirty by the afternoon and she is right. However, the evening makes it all ______.

A．favorable

B．worthwhile

C．precious

D．essential

可微函数的反函数一定可微，其导数与其反函数的导数互为倒数。

一国的需求偏好理论是如何提出的？为什么提出该理论？