根据句意用所给单词的适当形式填空。

Everyone should behave ____  in public. (polite)

 --Who's that boy standing over there?  --Sam, a foreign friend of____ . (I) 

After working all night, Kate couldn't stay____ the next morning. (wake)

The UK is an old ____ country, where there are many palaces and castles. (Europe)

Nothing would prevent UNICEF, an international charity,____ the living standards of the children in poor areas. (raise)

一个电阻两端加上30V电压时，通过它的电流是6A，现给它两端加上15V电压时，它的电阻是（）

与永磁体相比，电磁铁具有以下几个优点：
（1）电磁铁磁性的有无，可以由____ 来控制．
（2）电磁铁磁性的强弱可以由____ 来改变．
（3）电磁铁的N、S极是由____ 来决定．