Remote administration types are an example

问题：

Remote administration types are an example of one kind of (71) malicious software, the Trojan horse, or more simply Trojan. The purpose of these programs isn’t replication, (72) to penetrate and control. That masquerade as one thing when in fact they are something else, usually something destructive. There are a number of kinds of Trojans, including spybots, (73) report on the Web sites a computer user visits, and keybots or keyloggers, which record and report the user’s keystrokes in order to discover passwords and other confidential information.

RATS attempt to give a remote intruder administrative control of an infected computer. They work as (74) pairs. The server resides on the infected machine, while the client resides elsewhere, across the network, where it’s available to a remote intruder. Using standard TCP/IP or UDP protocols, the client sends instructions to the server. The server does (75) it’s told to do on the infected computer.

（74）处填（）。

A．W/S

B．S/C

C．B/S

D．C/S