曲柄连杆机构起什么作用？它有哪些主要机件？

October 1st, 2011

Dear Ann,

　　I hope that you and your children will be here in two weeks. My husband and I will  go to meet you at the train station. Our town is small but it is nice and beautiful. Your son Tom can go to the sports center every day. He can play games and go swimming there. Jill  is also lucky. My son has a cat and two sheep and I have two horses. She can play with them all day.

Please don't worry. I'm sure you’ll have a good time here.　See you soon.

Best wishes,

Linda

小题1:The letter was from ________________.

A．Ann

B．Linda

C．Jill

D．Tom小题2:Ann and her children will go to Linda’s home on about______________.

A．October 1

B．October 7

C．October 15

D．October 28小题3:Linda lives in ________________ .

A．a big city

B．a small town

C．a big town

D．a country小题4:Ann and her children are going to Linda’s home _____________.

A．by bus

B．by car

C．on foot

D．by train小题5:From the letter we know that Tom loves        and Jill loves          .

A．sports, animals

B．music, animals

C．sports, dancing

D．animals, sports

震惊全国的“三鹿奶粉”事件中的罪魁祸首是三聚氰胺（分子结构如图）．三聚氰胺是一种重要的化工原料，由于其含氮量高，且目前国际上又通用“测氮法”标定牛奶中蛋白质含量，于是一些不法商人就将其混入奶粉中以“提高”奶粉的品质．

（1）三聚氰胺的化学式为：______．

（2）三聚氰胺中氮元素的质量分数为______（保留一位小数）

（3）奶粉中蛋白质含量为15～20%，蛋白质中含氮量平均为16%，若不法分子在某品牌奶粉1袋（400 g）中加了1 g三聚氰铵，相当于增加了______g蛋白质．

（4）该事件后，许多人“谈化学物质色变”．请从“化学物质与人类社会的关系”角度，谈谈你对化学物质的认识（一句话即可）______．

喹诺酮类药物的作用靶点是抑制原核生物的DNA螺旋酶和拓扑异构酶IV。

下面哪些仪表能判断电缆障碍性质。（）

A、地阻仪

B、QJ-45电桥

C、数字万用电表

D、T-C300电缆故障综合测试仪

E、兆欧表

有如下两个关系，其中雇员信息表关系A的主键是雇员号，部门信息表关系B的主键是部门号。在雇员信息表关系A中，哪个属性是外键？[*]

A．雇员号

B．雇员名

C．部门号

D．工资