问题探究：

【1】新知学习

⑴梯形的中位线：连接梯形两腰中点的线段叫做梯形的中位线．

⑵梯形的中位线性质：梯形的中位线平行于两底，并且等于两底和的一半．

⑶形如分式 $\frac{m}{x+2m}$ （m为常数，且m＞0），若x＞0，则 $\frac{m}{x+2m}$ ，并且有下列结论：

当x 逐渐增大时，分母x+2m逐渐增大，分式 $\frac{m}{x+2m}$ 的值逐渐减少并趋于0，但仍大于0．当x 逐渐减少时，分母x+2m逐渐减少，分式 $\frac{m}{x+2m}$ 的值逐渐增大并趋于 $\frac{m}{2m}$ ，即趋于 $\frac{1}{2}$ ，但仍小于 $\frac{1}{2}$ ．

【2】问题解决

如图2，已知在梯形ABCD中，AD∥BC，AD＜BC，E、F分别是AB、CD的中点．

From:    annel@freemai14all.com    Sent: Wed., Oct. 19

To:      tss_liam@kidstarmail.net

Subject: Hello!

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Hi, Liam!

      So you're my new pen friend. Let me tell you a bit about myself. I'm 14 years old and I live in Calgary, CanadaI have two older brothers, Brian and Sam. I'm the only girl.

      I love sports and I'm always looking for exciting new hobbies to try. I like playing baseball in winter.

      It's fun beating the boys! But summer is my favourite time of the year. I love skateboarding and rock climbing in summer.

     Skateboarding's great because it's so fun and easy to learn! I often skateboard after school. There are many placesin the park where I can do stunts. I'm good at stunts like jumping and turning the skateboard!

     Rock climbing is also really fun. I usually climb with my dad on weekends. We can't do it on real mountains very often because we live in the city. We do indoor rock climbing instead but it's not as challenging.

    So that's me! How about you? Please write back soon!

Bye for now!

Anne　

我是聪明小裁判（下面各句怎样说更生动，在生动的句子后面打“√”，否则打×）

①弟弟抱着大西瓜，高兴极了。____

弟弟抱着大西瓜，高兴得摇头晃脑。____

②雨点又粗又大，打在地上“啪啪”响。____

粗大的雨点像鞭子一样毫不留情地抽打着大地。____

③灿烂的阳光没有使他苍白的脸红润起来。____

阳光没有使他的脸红润起来。____

读图，（a、b表示等压面），完成下列要求：