电冰箱使用的是三脚插头，当其工作时，如果接地线断了，则下列判断正确的是（   ）

如图所示，平行金属导轨宽度为L=0.6m，与水平面间的倾角为θ=37°，导轨电阻不计，底端接有阻值为R=3Ω的定值电阻，磁感应强度为B=1T的匀强磁场垂直向上穿过导轨平面．有一质量为m=0.2kg，长也为L的导体棒始终与导轨垂直且接触良好，导体棒的电阻为R_o=1Ω，它与导轨之间的动摩擦因数为μ=0.3．现让导体棒从导轨底部以平行斜面的速度v_o=10m/s向上滑行，上滑的最大距离为s=4m．（sin37°=0.6，cos37°=0.8，g=10m/s²），以下说法正确的是（   ）

2010年2月3日，******强调“毫不动摇地加快经济发展方式转变，不断提高经济发展质量和效益，不断提高我国经济的国际竞争力和抗风险能力。”从哲学上看，加快经济发展方式转变就必须          (　　)
①发挥主观能动性，贯彻落实科学发展观 ②按客观规律办事，突破经济规律的制约
③重视内因，提高自主创新能力        ④学会优化结构，推进经济结构调整

根据短文理解, 选择正确答案。

    "Haibao, the mascot(吉祥物) of the 2010 Shanghai World Expo, is very cute, "said Gu Hui, a school kid. "I want a big toy like the mascot."

    Haibao looks like the Chinese word ren, which means people or a person. The name, a typical lucky one in Chinese tradition comes from the Chinese phrase "Si Hai Zhi Bao" —the treasure of the four seas. It also means the treasure of Shanghai, which lies beside the sea.

    Haibao's blue curly(卷曲的) hair looks like the waves of the sea. Its smile is a sign of the healthy spirit of China. Those thumbs-up(翘拇指) will welcome millions of people to Shanghai from around the world. Its big feet show China has the ability to host a successful Expo.

    Haibao was created by two artists, one from the mainland(大陆) and the other from Taiwan. The design is about people living together in the city. The designers want it to fit the theme of the Shanghai Expo, that is, a good life should be created by all the people and people should have harmonious relationships(和谐关系) with nature and society, so that life in cities would be better.

    Surely the mascot will become the lucky symbol and cultural remark of Shanghai Expo.

原长为20cm的弹簧，一端固定，用10N的力拉另一端时，弹簧长度变为25cm，则这根弹簧的劲度系数为（　　）