清赵翼论某时期政制之变云：“迨至七国反后，又严诸侯王禁制，除吏皆自天朝，诸侯王惟得食租衣税，又多以事失侯，于是三代世侯、世卿之遗法始荡然净尽……。”材料论述的是哪一时期的史事  [ ]

A．战国

B．秦

C．西汉

D．东汉

All known techniques for handling complex problems successfully seem to fall into one of the three classes: subdividing the problem (51) , ignoring irrelevant detail in a safe way (52) , and having an independent agent (53) the internal consistency (contextual checking). The first two provide guidelines for solving the problem, the third serves to provide early warnings. A good programming language supports all three.
In subdividing problem, some of the subproblems may be similar to the (54) problem. It leads us to a (55) solution. This (55) solution is viable provided each of the subproblems is easier to solve than the original problem.

A. abrogation B. abstraction C. composition D. contraction