下列各项表述中正确的是

A．硫离子的核外电子排布式：1s²2s²2p⁶3s²3p⁴

B．NH₃、H₂O、CO₂、HCl分子中，CO₂孤对电子对最多

C．水分子的电子式：

D．次氯酸的结构式：H－O－Cl

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