在正方体ABCD﹣A₁B₁C₁D₁的各面的12条对角线中，与正方体的对角线A₁C垂直的共有____ 条．

阅读下文，思考并回答问题。

我交给你们一个孩子

张晓风

     ① 小男孩走出大门，返身向四楼阳台上的我招手，说：

     ②“再见！”

     ③那是好多年前的事了，那个早晨是他开始上小学的第二天。

     ④我其实仍然可以像昨天一样，再陪他一次，但我却狠下心来，看他自己单独去了。他有属于他的一生，是我不能相陪的，母子一场，只能看做一把借来的琴弦，能弹多久，便弹多久，但借来的岁月毕竟是有其归还期限的。

     ⑤他欢然地走出长巷，很听话地既不跑也不跳，一副循规蹈矩的模样。我一个人怔怔地望着巷子下细细的朝阳而落泪。

     ⑥想大声地告诉全城市，今天早晨，我交给你们一个小男孩，他还不知恐惧为何物，我却是知道的，我开始恐惧自己有没有交错？

     ⑦我把他交给马路，我要他遵守规矩沿着人行道而行，但是，匆匆的路人啊，你们能够小心一点吗？不要撞倒我的孩子，我把我的至爱交给了纵横的道路，容许我看见他平平安安地回来。

     ⑧我不曾搬迁户，我们不要越区就读，我们让孩子读本区内的国民小学而不是某些私立明星小学，我努力去信任自己的教育当局，而且，是以自己的儿女为赌注来信任——但是，学校啊，当我把我的孩子交给你，你保证给他怎样的教育？今天清晨，我交给你一个欢欣、诚实又颖悟的小男孩。 多年以后，你将还我一个怎样的青年？

     ⑨他开始识字，开始读书，当然，他也要读报纸、听音乐或看电视、电影，古往今来的撰述者啊，各种方式的知识传递者啊．我的孩子会因你们得到什么呢？你们将饮之以琼浆，灌之以醍醐，还是哺之以糟粕？他会因而变得正直、忠信，还是学会奸滑、诡诈？当我把我的孩子交出来，当他向这世界求知若渴，世界啊，你给他的会是什么呢？

     ⑩世界啊，今天早晨，我，一个母亲，向你交出她可爱的小男孩而你们将还我一个怎样的呢？

下列物质的用途中，利用了它的物理性质的是(     )

阅读下列短文，从每题所给的 A、B、C 和 D 四个选项中，选出最佳选项。
    A high school senior from Houston, Texas, was accepted by each of the 20 top-ranked universities to which he applied — and was offered a full scholarship to every single one of them.
    Michael Brown, a 17-year-old student at Lamar High School, went viral（迅速成名） after he was caught on camera screaming in glee upon learning he was accepted into Stanford University in December.
    Little did the teen know at the time, but his excitement would increase by a factor of 20 in March when he was also accepted into Harvard, Princeton, Yale, the University of Pennsylvania, Georgetown, Northwestern, Vanderbilt and the University of Michigan, among other prestigious（著名的） colleges.
    But what did it take for Brown to pull off his flawless（完美无瑕的） clean sweep?
    To start, the high schooler has an impressive 4.68 grade point average and an SAT score of 1540 out of 1600. His ACT score, a 34 out of a possible 36, proved to be just as excellent. Brown's extracurriculars also include various internships as well as participation on his high school's debate team.
    His mother, Berthinia Rutledge-Brown, told The New York Times that she was simply blown away by her son's perfect performance. "He actually earned it," she told the Times. “I always knew Mike would get into a good school. I always knew he'd get good scholarship support. But I never imagined this."
    So, which school will he be attending this fall? Although Brown remains undecided at the moment, he reportedly plans to major in political science and hopes to one day become a lawyer.
    He will make the big decision by May 1.

在“测定小灯泡电功率”实验中，电源电压为4.5V，小灯泡额定电压为2.5V，如图所示，某实验小组选择合适器材后进行实验，试回答：