如图所示，距离为L的两块平行金属板A、B竖直固定在表面光滑的绝缘小车上，并与车内电动势为U的电池两极相连，金属板B下开有小孔，整个装置质量为
据报道，美国哥伦比亚大学的社会学家利用互联网技术做了一次实验，证明只要通过“电子邮件的6次信息接力”，一个人就可以同世界任何一个陌生人
已知函数． （1）若对于区间内的任意，总有成立，求实数的取值范围； （2）若函数在区间内有两个不同的零点，求： ①实数的取值范围； ②的取值
下列事实能说明铝的金属活动性比铁或铜强的是（ ） A．铝在地壳中含量比铁高 B．铝的熔点低于铜的熔点 C．空气中铁比铝更容易被腐蚀 D．铝丝在硫
阅读下面短文，回答问题。（可以用完整句子回答，也可简答） December 25th is Christmas Day. In most countries it is the most important （重要的） day in the year. All
They _______ Tom to record the hit single. A. kept up with B. caught up with C. put up with D. teamed up with
They sat down opposite each other, but it was some moments ______ they spoke. A. after B. before C. since D. when
I often recall those good old days. At that time life was relatively simpler, and people were much more 41 and gentler. Recently, to my surprise, I got the opportunity to experience that same war
的值。
