(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.

（68）处填（）。

A．OSPF

B．RIP

C．RARP

D．BGP

下列哪一项是葡萄胎特异性声像图表现（）

A.子宫大于孕周

B.双侧出现黄素囊肿

C.宫腔见蜂窝状无回声区

D.子宫肌层回声不均

E.胎囊形态不规则