For each blank, choose the best answer from the four choices and write down on the answer sheet.
(11) is a protocol that a host uses to inform a router when it joins Or leaves an Internet multicast group.
(12) is an error detection code that most data communication networks use.
(13) is an interior gateway protocol that uses a distance vector algorithm to propagate routing information.
(14) 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.
(15) is an identifier of a web page.

A．4B/SB

B．CRC

C．Manchester Code

D．Huffman Code

建设资源节约型、环境友好型社会在我国的现实紧迫性有（）。

A、我国人口多给资源环境带来重大压力

B、我国资源相对不足、资源消耗高、资源利用效率低已严重制约经济社会的发展

C、环境污染和生态破坏严重制约经济社会发展，威胁着人的生存和发展

D、以上都是