我们知道，顺次连接任意四边形各边中点所得四边形是平行四边形，那么顺次连接等腰梯形各边中点所得四边形是什么特殊四边形呢？探索并证明你的结论．
是菱形．
如图，梯形ABCD，AD=BC，且点E，F，M，N，分别是四边形的中点，则四边形EFMN是菱形．
证明：∵四边形ABCD是等腰梯形，且点E，F，M，N，分别是四边形的中点，
∴EF=MN=
BD，FN=EM=1 2
AC，1 2
∵梯形ABCD，AD=BC，
∴AC=BD，
∴EF=MN=FN=EM，
∴四边形EFMN是菱形．
| 完形填空. | |||
| Some people who find themselves unable to solve a problem react by just giving up.But it is not good to__1__from problems by giving up or by making__2__for failure.You may be sure that all young people go through the same__3__process that you are going through :__4__new situations,developing new skills,and testing their abilities. In many cases,we only "think" there is no__5__to a particular problem.But__6__we can overcome the problem and achieve the goal by making a direct attack. __7__,a boy wanted to be a debater.When he__8__for the debating team as a freshman,the coach thought he was _9__.He was shy；he had a high pitched (音调) voice；and his posture (仪态) was poor.By his junior year,he__10__the school debating team,and in his senior year he was__11__the team in his state.He achieved his goal because he had made a direct attack upon his problem. __12__attack is often the best way to meet problems,we have to be realistic in judging situations.__13__it is necessary to __14__either the tactics (策略) or the goal. A boy who wants to be a great football player may be too light and not quite __15__ for football.In this situation,becoming a great football player may be an __16__goal for him.__17__,he may become outstanding in tennis or golf,and__18__his desire to take part in sports. So,although direct attack is often the best way to __19__ problems,it is important to study the_20__and make a wise decision about what to do. | |||
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