I want to _____________a policeman. [ ]_爱下问搜题

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问题选择题

I want to _____________ a policeman. [ ]

A. is

B. be

C. are

答案

答案：B

选择题

It’s getting dark, please _______the light.

A．turn off

B．turn on

C．turn up

D．turn down

问答题

设

具有连续的二阶偏导数，且满足

，试求函数u的表达式．