题目

One of the greatest benefits of Internet friendships is that they are based on common interests, rather than a________ ,age or popularity. 答案：appearance计算：（1）-6ab+ba+8ab；           （2）（5a-3b）-2（a-2b）；（3）3a+（8a-2）-（3-4a）；      （4）3x2-[7x-（4x-3）-2x2]．