先化简，再求值：3x²y﹣2x²﹣（xy²﹣3x²y）﹣4xy²，其中|x|=2，y=$\frac{1}{2}$，且xy＜0．

    ①父亲的准备是十分漫长的。他今天从地里捡回一块砖，明天可能又捡进一片瓦，再就是往一个黑瓦罐里塞角票。虽然这些都很微不足道，但他做得很认真。

    ②于是，一年中他七个月种田，四个月去山里砍柴，半个月在大溪滩上捡屋基卵石，剩下半个月用来过年、编草鞋。

    ③大热天父亲挑一担谷子回来，身上着一片大汗，顾不得揩一把，就往门口的台阶上一坐。他开始“磨刀”。“磨刀”就是过烟瘾。烟吃饱了，“刀”快，活做得去。

    ④台阶旁栽着一棵桃树，桃树为台阶遮出一片绿阴。父亲坐在绿阴里，能看见别人家高高的台阶，那里栽着几棵柳树，柳树枝老是摇来摇去，却摇不散父亲那专注的目光。这时，一片片旱烟雾在父亲头上飘来 飘去。

    ⑤父亲磨好了“刀”。去烟灰时，把烟枪的铜盏对着青石板嘎嘎地敲一敲，就匆忙地下田去。

    ⑥冬天，晚稻收仓了，春花也种下地，父亲穿着草鞋去山里砍柴。他砍柴一为家烧，二为卖钱，一元一担。父亲一天砍一担半，得一元五角。那时我不知道山有多远，只知道鸡叫三遍时父亲出发，黄昏贴近家门口时归来，把柴靠在墙根上，很疲倦地坐在台阶上，把已经磨穿了底的草鞋脱下来，垒在门墙边。一个冬天下来，破草鞋堆得超过了台阶。

    ⑦父亲就是这样准备了大半辈子。塞角票的瓦罐满了几次，门口空地上鹅卵石堆得小山般高。他终于觉得可以造屋了，便选定一个日子，破土动工。

   Have you ever seen a movie called “ The Choir Boys”(《放牛班的春天》)？The French movie tells the story of a group of naughty boys who learn music from a dedicated(尽职的) teacher. In Shanghai, there is also a group of children learning music. But their story is a bit different.
   The musical group, “Shepherds'Kids” , was founded(建立) by the Shanghai Jiuqian Volunteer Center. There are about 40 students in this group. Their parents are migrants(打工者) working in Shanghai.“ The music courses are free,” said Zhang Yichao, founder of the group. “We just want to make the children's lives more colorful.”The kids learn singing, dancing and musical instruments. Their teachers are volunteers from high schools.Learning music is not an easy job, especially for these migrant workers' children.“I never know the musical stave(五线谱) before,” said Hua Delong, 13. “Sometimes it was really hard to study.”Tang Yue is a volunteer teacher at the center. She is a student from Shanghai Ping'he Bilingual High School.“These kids face difficulties bravely,” said Tang. “Sometimes they have to help their parents do housework and have little time to practice, but I never hear them complain.”
   Their hard work has paid off(回报). Today many people know the group. They have even performed as a choir for foreign pop stars.
Li Luo, 14, told “ Teens” how appreciative she was of the group.“I had little fun before. I seldom(很少) watched TV. Study seemed the most interesting thing in my life. “Shepherds' Kids has given me a new life.”