OSI参考模型和TCP/IP协议体系分别分成几层（）。
A、7和7
B、4和7
C、7和4
D、4和4
参考答案：B
按照要求进行句型转换。
1. She is doing her homework. (改为否定句)
She __________ __________ her homework.
2. They are looking at the blackboard. (改为一般疑问句)
__________ __________ __________ at the blackboard?
3. Tom is playing basketball. (对画线部分提问)
What __________ __________ __________?
具有季铵结构的M乙酰胆碱受体拮抗剂为
A．溴丙胺太林(Propantheline Bromide)B．贝那替秦(Benactyzine)C．盐酸苯海索(Trihexyphenidyl HY-drochloride)D．哌仑西平(Pirenzepine)E．美加明(Mecamvlamine)
