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问题 选择题

顺次连结四边形四边中点所得的四边形一定是（   ）

A．平行四边形

B．矩形

C．菱形

D．正方形

答案

答案：A

根据三角形中位线定理，可知边连接后的四边形的两组对边相等，再根据平行四边形的判定可知，四边形为平行四边形．故选A

选择题

已知▱ABCD，添加下列一个条件：①AC⊥BD②∠BAD=90°③AB=BC④AC=BD，其中能使▱ABCD是菱形的为（　　）

A．①③

B．②③

C．③④

D．①②③
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单项选择题

Everybody dreams. Some people think dreams can tell us about the future. Other people think dreams can tell us about ourselves. It’s like our (11) is talking to us.

Why are dreams (12) strange and hard to understand Some people think our brain uses (13) to talk to us. When we fly, swim, or fall down in our dreams, it has a (14) meaning. Lots of doctors help people (15) their dreams. They find that dreams tell us about our (16) and fears.

These days, many scientists (17) that dreams are very important. During the day, we have many (18) , and our brain receives a lot of information. When we dream, our brain (19) information that is not important, and puts the most important information into our (20) . As we learn more about the brain, we may find answers to our questions about dreams.

13().

A.symbols 

B.examples 

C.numbers 

D.pictures
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