导体的电阻是由导体的材料、___________和___________决定，滑动变阻器是通过改变接入电路导体的__________来改变电阻的。
Caroline doesn't have a gift for music, but she ________ it with hard work. A. goes back on B. takes away from C. makes up for
1 kg铀全部裂变释放出的能量约为8.5×1014 J，相当于完全燃烧多少无烟煤释放的能量？（无烟煤的热值为3.4×107 J/kg）
Helen always helps her mother even though going to school _____ most of her day． A．takes up B．makes up C．saves up D．puts up
Two thieves came to a house to steal something, they dug a hole in the wall of the house. There lived many mice in the house. The woman in the moonlight saw a mouse crawl(爬行) into the ho
将物体受到两个共点力和合成为一个力，下列说法正确的是（ ）A．是物体实际受到的一个力B．单独作用时与和共同作用的效果是相同的C．的大小
根据表中的信息判断下列说法正确的是( )。 物质金刚石石墨 外观无色，透明固体灰黑，不透明固体 熔点？？ 燃烧热/(kJ·mol－1)395.4393.5 A．表
下图是两个生态系统中腐殖质总量随时间而发生变化的情况，甲、乙曲线分别代表哪两个生态系统？ A. 热带雨林、温带森林 B. 温带草原、
，求
的值．
．