已知a²+ab=5，ab+b²=﹣2，a+b=7，那么a﹣b=____ ．

下列四部反映晚清历史的影视，按历史事件的发生先后顺序排列，正确的是（    ）

①《末代皇帝》②《鸦片战争》③《甲午风云》④《火烧圆明园》

①当x=1.7时，x+（x）+x）=6；

②当x=﹣2.1时，x+（x）+x）=﹣7；

③方程4x+3（x）+x）=11的解为1＜x＜1.5；

④当﹣1＜x＜1时，函数y=x+（x）+x的图象与正比例函数y=4x的图象有两个交点．

长白山地主要的经济活动是（    ）

Teenagers growing pains

    Today, our students are facing many different problems and they want to ask some experts for help. Nancy says she feel stressed these days because of too much homework. She hasn't enough time to sleep for a long time and often falls asleep during the classes. John says he doesn't like to study because of the bad effect of computer games. Cindy says she gets fat because she likes to eat junk food and hardly ever takes exercise. Frank has the worst problem. He always fights with others as he doesn't know how to get on well with others and few of his classmates would like to talk with him.