last-2-2-9 怎么搞清楚充分/必要条件

9. Governments have only response to public criticism of socially necessary services regulation of the activity of providing those services. But governments inevitably make the activity more expensive by regulating it, and that is particularly troublesome in these times of strained financial resources.However, since public criticism of child-care services have undermined all confidence in such services, and since such services
are socially necessary, the government is certain response.
Which one of the following statements can be infered from the passage?
A).The quality of child care will improve.
B).The cost of providing child care services will increase.
C).The government will use the funding to foster the advances in child care.
D).If public criticism of policy is strongly voiced, the government is certain to respond
E). If child care services are not regulated, the cost of providing child care will not increase.
The answer is B.

文章的的推理是这样的:

1.政府只对有必要的服务进行回应,并作出规定.
2.政府进行规定的服务成本都会增加.
3. child care service 是政府必须作出回应的服务.

因此, child care service 的成本会提高.
用无关词排除法可排除A、C、D（因为归纳题只要是文中没有提供的信息均是无关选项）。

E是原文的否命题，不正确。 只有逆否命题才是等价的。

想确证一下,这里的government responds 与necessary service 是不是充分条件.我经常搞不清楚怎么区分充分条件,必要条件,以及充分必要条件.道理我都清楚,可一做题目就晕.这里的Governments have only response to public criticism of socially necessary services 是怎么推得:

If 必要服务then 政府回应  A--->B  A 是B 的充分条件 还是说

Only if 必要服务, then政府回应. B--->A  B 是A 的必要条件?

有没有什么系统的文章可以介绍,我恶补一下?

第一句话说的是GOVERNMENT RESPONSE 与PUBLIC CRITICISM 之间的关系, 看不出来GOVERNMENT RESPONSE 与NECESSARY SERVIE 之间的关系，而且也不用管它是怎么来的，这句话是摆在那里的一个PREMISE, 不是结论