选出与例词不同类的单词。swing:

在方程组$\left\{\begin{array}{c}2x+y=1-m\\ x+2y=2\end{array}\right.$中，若未知数x，y满足x+y＞0，则m的取值范围在数轴上的表示应是如图所示的（　　）

假定英语课上老师要求同桌之间交换修改作文, 请你修改你同桌写的以下作文。文中共有10处语言错误, 每句中最多有两处。每处错误仅涉及一个单词的增加、删除或修改。

增加：在缺词处加一个漏字符号（∧）, 并在其下面写出该加的词。

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限一词；2. 只允许修改10处, 多者（从第11处起）不计分。

Dear Peter,

    I'm writing to tell you something about e-hongbao, that is very popular in China.

    E-hongbao is actual a kind of lucky money from and to relatives and friends during festivals or in special occasions. For many young people, grabbing e-hongbao on our mobile phones is a fairly exciting activity. Unlike the tradition of elders give lucky money to children, over half of the people sending e-hongbao is in their 20s. It's just for fun but giving best wishes, while the sum of money matters a little. In a word, e-hongbao is bringing new color to the old tradition.

    Now I'm concerned about the safe of online payment, and rules and regulations needed to be improved to guarantee its operation.

Best wishes.

Yours,

Li Hua

到北京的距离大约是5×10²km，如果将来要建成高速铁路，列车速度可达3×10²km/h，到那时如果我们要从赤峰坐高铁直达北京，列车按此速度运行需要的时间是（　　）