(66) is a protocol that a host uses to inform a router when it joins or leaves an Internet multicast group.

(67) is an error detection code that most data conlmunication networks use.

(68) is an interior gateway protocol that uses a distance vector algorithm to propagaterouting information.

(69) is a transfer mode in which all types of information are organized into fixed form cells on all asynchronous or nonperiodic basis over a range of media.

(70) is an identifier of a web page.

（69）处填（）。

A．ISDN

B．x.25

C．Frame Relay

D．ATM

判断。（对的打“√”，错的打“×”）

1．在减法中，差比被减数、减数都小。[ ]

2．三位数加三位数的和有可能是三位数，也有可能是四位数。[ ]

3．最大的三位数与最小的四位数的和是1999。[ ]

4．在加法中，和总比两个加数都大。[ ]

5．一个数与356相加，和是721，求这个数，列式是356+721。[ ]