For each blank，choose the best answer from the four choices and write down on the answer sheet．

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

(2) is an error detection code that most data communication networks use．

(3) is an interior gateway protocol that uses a distance vector algorithm to propagate routing information．

(4) is a transfer mode in which all types of information are organized into fixed form cells on an asynchronous or non -periodic basis over a range of media.

(5) is an identifier of a web page.

4（）

A．ADSL

B．ATM

C．Frame Relay

D．DDN

原位癌与浸润癌的主要区别在于

A．肿瘤大小

B．边界清晰程度

C．基膜是否受侵犯

D．淋巴管有无癌栓

E．有无浸润血管