For each blank, choose the best answer from the four choices and write down on the answer sheet. （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 communication networks use. （68） is an interior gateway protocol that uses a distance vector algorithm to propagate routing information. （69） 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. （70） is an identifier of a web page.

70（）

A．HTTP

B．URL

C．HTML

D．TAG

离心式风机前弯叶片可以获得（）。

A．较高的压力

B．较低的压力

C．稳定的风力