WTO的成立是世界政治多极化的重要表现之一。(   )

    My name is Bill. I'm from England. I am a worker. I work in a clothes shop. My wife , Ann, is a teacher. She teaches English in a junior high school. We have two kids: a son and a daughter. They are students. Jim is our son. Now he is in his favorite T-shirt and blue pants. Sally is our daughter. She likes blue very much. Now she is in her blue dress. My father's name is Robby. My mother's name is Diana. They are old and they don't work now. I have a brother. His name is Robert. He is a worker, too. My wife's father is Sam. Her mother's name is Rose. Her sister is Lily. She is a teacher, too.

先化简，再求值：﹣a²b+（3ab²﹣a²b）﹣2（2ab²﹣a²b），其中 a=﹣1，b=﹣2．