在一个单项式中，所有字母（），叫做这个单项式的（）。
若关于y的方程是一元一次方程，则a=___
B）翻译（共5小题，计10分）阅读下面的短文，将划线句子翻译成中文。51.Today life is much better than before. Vision phone(可视电话) is used in some provinces. Maybe it will be used in every family. People can have an examination about their health without a doctor or a nurse in the room. 52.Now some people do some shopping at home.53.And how about our education？ There have been more educational(教育的) programs on the radio， on TV or on the Internet. Some children live very far away from their schools， more and more of them don’t need to go to school every day now. They can study at home. 54.Teachers teach them on the Internet.In the future， each family will have a robot. 55.Robots will help people with their housework. In some years people can have a trip on the moon and some people can live under the sea in hot summer.51.Today life is much better than before
1-2+3-4+5-6+…+2007-2008=______．
化简和求值。（1）2a-5b-3a+b；（2）2x+（5x-3y）-2（3x+y）；（3）3（4x2-3x+2）-2（1-4x2+x）；（4）求多项式3y2-x2+（2x-y）-（x2+3y2） 的值，其中x=1，y=-2。
化简：（5a2+2a﹣1）﹣4（3﹣8a+2a2）
根据幂的意义，（-3）4表示______，-43表示______．
若（x-3）2+|2y+1|=0，则x-y=______．
解二元一次方程组2m+7n=5(1)n=3m-2(2)把（2）代入（1）消去n，得到关于m的一元一次方程为______．
若|a+2|与（b-3）2互为相反数，则ab+a×（3-b）=（）。