一个梯形的周长是20厘米，上底是5厘米，一条腰长3厘米，一条腰长4厘米，则下底长
题型：填空题
问题：
一个梯形的周长是20厘米，上底是5厘米，一条腰长3厘米，一条腰长4厘米，则下底长（ ）。
题型：填空题
短文改错 (共10分,每小题1分,满分10分)
文中共有10处语言错误，要求你在错误的地方增加、删除或修改某个单词。
增加：在缺词处加一个漏字符号( ＾), 并在此符号下面写出该加的词。
删除：把多余的词用斜线划掉。
修改：在
错的词下划一横线, 并在该词下面写出修改后的词。
注意:：1、每处错误及其修改均仅限一词；
2、只允许修改十处, 多者(从第11处起) 不计分。
Many young boys and girls had the habit of smoking, though they are middle school student. As we all know, smoking do harm to human beings. More and more people have realized th
at how serious this problem is. But they are never boring with i
t. Some people think smoking is a kind of fashion, and other think smoking can refresh himself . In fact, smoking causes many illnesses. The most serious illness led by smoking is lung cancer. Meanwhile, smoking is the waste of money. What’s worse, careless smokers may cause danger fires.