人类生活和生产都离不开金属．

某些试剂能使生物组织中的有关化合物或结构产生特定的颜色反应，以下对应关系错误的是（ ）

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    This is Hong Kong Middle School. It is very big and beautiful. There are 34 classes, 300 teachers and 3, 500 students in the school. In the middle of the school there is a tall building. It's for us to have classes. All the classrooms are there. There are some small rooms, too. They are offices for the teachers to work. All the teachers get ready for their lessons there.

    In front of the tall building, there is a small one. It is the library. There are many books there. The teachers and the students like to read books in it. Sometimes they borrow(借)books from it.

    There is a dining hall behind the tall building. Some of the students have lunch in it.

    I like my new school very much.

（Ⅰ）若a=2，b= $\frac{5}{2}$ ，求cosC的值；

（Ⅱ）若sinAcos² $\frac{B}{2}$ +sinBcos² $\frac{A}{2}$ =2sinC，且△ABC的面积S= $\frac{9}{2}$ sinC，求a和b的值．