对应OSI的网络层协议有　　Ⅰ．IP协议和Internet控制报文协议　　Ⅱ．地址转

l. Next to Simon's high school is a river that is 30 meters wide. Students can cross the river by walking

over a bridge. One-fifth of the length of the bridge goes over land on one side of the river, and one-fifth

of the length of the bridge goes over land on the other side of the river. What is the total length of the

bridge?

Answer: _                                                                        

2. There is a new film,  the price of which is 20 dollars for each adult and 10 for each child; if you buy

three tickets or more you will have a 10% discount; Susan, a primary school student, together with her

parents is going to see the film. How much will they pay?

Answer: _                                                                        

根据《煤炭可浮性评定方法》MT259-1991标准，Ec为90.0%的煤泥可浮性为易浮。

在制作人口腔上皮细胞临时装片时，不用清水而用生理盐水，主要是为了[ ]

A．保持细胞的正常形态                  

B．杀死细胞      

C．杀灭细菌                            

D．使口腔上皮细胞分散开

患儿8岁，前牙深覆合，第一恒磨牙萌出2／3，应重点防治哪个牙齿

A．第一乳磨牙

B．第二乳磨牙

C．尖牙

D．第一恒磨牙

E．第二恒磨牙

儿童时期各种心身发育最快的时期是( )

A．新生儿期
B．乳儿期
C．婴儿期
D．幼儿期