除气器短期停止工作时，只将（）与砂泵蝶阀关闭，维持运转。
A.真空泵进气阀
B.真空泵排气阀
C.真空泵进、排气阀
D.真空泵进、排液阀
参考答案：C
现定义一种运算：a*b=ba-a+b．
试计算：
（1）2*3
（2）4*（-3）
(41) is a protocol that a host uses to inform a router when it joins or leaves an Internet multicast group. (42) is an error detection code that most data communication networks use. (43) is an interior gateway protocol that uses a distance vector algorithm to propagate routing information. (44) 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. (45) is an identifier of a web page.
A．4B/5B
B．CRC
C．Manchester Code
D．Huffman Code
