english:be careful with such things.if you __,you will drop them A.don't B.aren't

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• english:be careful with such things.if you __,you will drop them A.don't B.aren't
• 用所给词的适当形式填空.1..It's dangerous to stand outside,for the wind is blowing____(strong).2.English is ______(wide) used in the world.3.They don't know why you talked to them so_______(angry).4.It is raining ______(heavy),so you"d better not go out now.5.He did the work as ______(careful) as most of us.6.Li Lei and Lin Tao are working much ____(hard)than before.
• In learning English,one should first pay attention to listening and speaking.It’s the groundwork(基础) of reading and writing.You’d better  try your best to speak while you are doing much listening.Don’t be   afraid   of making mistakes.But be careful not to let them stop you from improving your   English   .While you are doing this,a good   way   is to keep a diary,write notes or letters.Then if you can,ask some others to go through   what   you have w
• 单缝衍射,缝宽a=0.2mm,透镜焦距f=20cm白光垂直入射观察屏上x=1.2mm处为明纹中心,求该明纹对应的波长
• 求个证明:无穷大的数的倒数是无穷小的数