Do equations and historical( 历史的) facts give you a headache? A change in the school timetable(课程表) may be the cure.

    This  suggestion  is  based  on  a  recent  study  carried  out  by  scientists  from  Royal  Holloway, University of London, the UK. They found that teenagers could get higher marks in math if they studied in the mornings and better grades in history if they were taught in the afternoons.

    The researchers studied students' grade reports, class timetables and absence rates( 缺席率) at a middle school in Bulgaria over nine years. The results showed that when teenagers had math classes earlier in the day, they scored about 7 percent higher in tests than when taught in the afternoon. Lower-ability students feel stressed most when they were studying math in the afternoon. In history, students taught in the afternoon scored about 6 percent higher than when they were taught in the morning. However, there was no sign that similar patterns( 模 式 ) work for other subjects such as languages or geography.

    Velichka Dimitrova, who did the study, said the findings show that we perform( 表 现 ) better at different times of the day. “In the morning, our brains are better and fresher, so we are better at doing something like problem solving, where we require more speed and attention” Dimitrova told The Telegraph. “In the afternoon, it seems that this process slows down. On the other hand, history is more suitable for the afternoon, when we are more creative and open to discussion,” she said. Subjects such as foreign languages require both memory and creativity. This is perhaps why the time of day had no influence on language learning.

    Time-of-day influences such as these are believed to have something to do with the body clock.

    This is the system in our bodies that controls when we need to sleep. Some schools in the US and UK have tried later school starting times for teenagers, whose body clocks change as they grow into adults. Dimitrova believes schools should jump at this chance to improve their students' performance just by changing their timetables.

已知$\left|\overrightarrow{a}\right|=3,\left|\overrightarrow{b}\right|=4$，且$(\overrightarrow{a}+k\overrightarrow{b})\perp (\overrightarrow{a}-k\overrightarrow{b})$，则k等于             (     )

    A boy couldn't speak when he was 3 years old. A lot of people thought he was a foolish boy. When the boy was 9 years old, he could speak but he still couldn't speak well. His teacher didn't like him at all and his classmates laughed at him. He felt very sad, One day his father had a walk with him. They went to a wood and there were a lot of trees there. Then his father took him to two trees and said to him.“Boy, this tree is sabal (菜棕，一种树的名字）and this tree is fir(冷杉). Sabal grows very quickly at first but a few years later, it will stop growing, so the tallest Sabal can't reach(达到）ten meters. But the fir is different, it grows very slowly at first but it never stops growing so it can grow very tall."

    Then his father took him to another fir. It was so tall, so strong. It can reach the sky. The father said to his son, “Son, you are the fir."The boy understood his father's words. The boy became a very great scientist. Do you know who he is? He is the world-famous scientist. His name is Einstein.

      阅读下面文段后按要求答题。    
                                                                                                父亲的眼神
      ①一个背影，让朱自清潸然泪下；一个眼神，让我终生悚然汗下。
      ②那是在我上高中时，尽管我的语文、英语成绩居班里前凡名，但是数理化成绩却出奇地差。在这样的情况下，自己估计高考肯定无望，因此，高一期末考试后，我彻底失望，决定回家务农。
      ③因自觉惭愧，回到家后听说父亲正在田里拔草，我赶紧戴上草帽，赶到田里帮忙。学都上不好，再不勤快一点，会被人骂为“混混”的。顶着烈日，到了田里，我告诉父亲，不想再上学，反正学不好了，还不如回家种田。
      ④我以为父亲会勃然大怒，因为母亲去世较早，这些年来他节衣缩食，对我寄予了很大的希望，当了一辈子的“睁眼瞎”，他不想我走他的老路。但是，父亲始终埋着头，并不理会我，好像并没有听我讲的话。我不敢再说话了，只好随着他卖力地拔草。近晌午的太阳很毒，汗水不住地渗出来，衣服贴在身上，抬起头，父亲仍然在埋头拔草，我怎好意思停下来。 
      ⑤中午，回家吃饭，父亲仍然没有就我辍学的事发表意见。让我说什么好?情况很不妙，我知道，越是在闷热干燥的夏日午后，越会有突如其来的狂风暴雨。这即将燃烧的沉默，真让我忐忑不安。
      ⑥这时父亲对我说：“走吧，去地里把瓜秧翻一下，要不夸年地瓜就没收成了。”我爽快地拿起锄头就走。我就不信，父亲能干，自己就不行！
      ⑦夏目午后的太阳实在太厉害了，汗水把我迷糊得睁不开眼睛。要在学校，正是午睡的时候，而现在；我早已经呵欠连天了。看看我的老父亲，光着黑黝黝的脊梁，仍在埋头翻秧——趁着父亲不注意，我跑到树阴底下枕着锄头就睡着了。
      ⑧好像没过多大一会儿，我就被父亲推醒。睁开眼，我看到父亲冷冷的眼神，那眼神很复杂，既有悲哀、绝望，更有期盼和激励，还有许多我一下子读不出的内容……
      ⑨“娃儿，种庄稼也像做学问，如果你不上心，啥子事情都干不好。你在地头睡觉，庄稼也会在田里‘睡觉’……”
      ⑩父亲的眼神让我受不了，我的后脊早已经汗流下来了，不是热汗，是冷汗。当天晚上，回到家，我觉得浑身骨头都散了。摸着胳膊上已经晒脱了皮的地方，我的心乱成一锅粥。
      ⑪第二天早上，天刚蒙蒙亮，父亲又轻轻把我叫醒。一睁眼，除了看见他瘦弱的躯体、苍老的面容外，又是郅特有的眼神。想到父亲近70岁了，身体多病，为供我读书，每天仍在田间地头躬亲劳作，毫无怨言……这时，我突然坐起来，大声地喊了一句：“我要上学!”   
      ⑫后来的事情变得很简单。高考后，我上了大学中文系。再后来，到电视台当上了一名记者。        
      ⑬尽管远离了家乡，远离了父亲，但那熟悉的眼神始终占据了我的记忆。今夜回想起来，仍然抑制不住自己汹涌的感情。走到院子外，望着深速的苍穹和满天的繁星，我不由喃喃自语：“山一样沉默的父亲啊，你的期盼，你的鞭策，你的激励，终于成就了我的今天，我水远也忘不了你的眼神!"

      (文段有删改)