若2xm-1y2与-2x2yn是同类项，则（-m）n=______．
由同类项的定义可知n=2，m=3，
则（-m）n=（-3）2=9．
It was early morning in London _____ Prime Minister Cameron arrived to give his speech.
A．where
B．when
C．while
D．that
敷面分（）两种，。
