下列说法正确的是( ) A．SiH4比CH4稳定 B．O2－半径比F－的小 C．

短文改错。

     I am a very active girl in my class.I have many hobby, such as writing stories, playing

piano and singing English songs.My most favorite subject is English.I became interest in it

when I was very young.My dream is to study abroad.But now I need to improve my English

and learn more about west culture as well.I will be able to improving the friendship between

China and the rest of the world.I hoped my dream will come true.And I believe in nobody can

change my mind.I will work harder and follow my heart, no matter how happens!

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娃哈哈矿泉水每瓶售价1.2元，现甲、乙两家商场给出优惠政策：甲商场全部9折，乙商场20瓶以上的部分8折，若你是消费者，选哪家商场购买比较合适？

已知xy²=﹣2，求（x²y⁵﹣2xy³﹣y）（﹣3xy）的值．

将一物体以速度v从地面竖直上抛，取地面为零势能面，当物体运动到某高度时，它的动能恰为重力势能的一半，不计空气阻力，则这个高度为            （     ）

A．v²/g

B．v²/2g

C．v²/3g

D．v²/4g

投冷却器时，应（）。

A.先开热油进口

B.先开热油出口

C.先开冷却水进口

D.先开冷却水出口