儒家____        无为而治

法家____        兼爱非攻

道家____        知己知彼，百战不殆

墨家____        用“刑罚”统治

兵家____        以礼治国

    Do teenagers in small villages do chores at home? How about the teenagers in big cities? Here is a survey. We asked 4,000 teenagers in China several questions. Half of them come from big cities like Beijing, Shanghai and Guangzhou. The others are from small villages. We made a diagram of the result of our survey. Let's have a look at it. We found out that teenagers from small villages do more chores than those from big cities. Maybe it is because they live a harder life. Our advice to parents in big cities is that parents should give their children some chores to do. Doing chores teaches teenagers to take care of themselves.

    Chores 2000 teenagers in small villages.

    Chores 2000 teenagers in big cities

小明出水痘，老师让他回家休息，这属于预防传染病的哪一措施（    ）

将一电荷量为+Q的小球放在不带电的金属球附近，所形成的电场线分布如图所示，金属球表面的电势处处相等．a、b为电场中的两点，则（   ）