“在政府组织上，他给中国历史王朝奠定了权威性的规范，使得以后几百个帝王只能在其所想到的圈子里作潇潇的修正，而无力作巨大的改变。”“他”是指（　　）

如图，质量为M的足够长金属导 轨abcd放在光滑的绝缘水平面上．一电阻不计，质量为m的导体棒PQ放置在导轨上，始终与导轨接触良好，PQbc构成矩形．棒与导轨间动摩擦因数为μ，棒左侧有两个固定于水平面的立柱．导轨bc段长为L，开始时PQ左侧导轨的总电阻为R，右侧导轨单位长度的电阻为R₀．以ef为界，其左侧匀强磁场方向竖直向上，右侧匀强磁场水平向左，磁感应强度大小均为B．在t=0时刻，一水平向左的拉力F垂直作用于导轨的bc边上，使导轨由静止开始做匀加速直线运动，加速度为a．

6×____＜40

____×7＜23

阅读下面短文， 从短文后各题所给的四个选项 （A、B、C、D ）中，选出可以填入空白处的最佳选项。

    Jenna, a popular girl from Westwood Middle School, had graduated first in her class and was ready for new 1 in high school.

    2, high school was different. In the first week, Jenna went to tryouts (选拔赛) for cheerleaders (拉拉队队员). She was competing against very talented girls, and she knew it would be 3 for her to be selected. Two hours later, the 4 read a list of the girls for a second tryout. Her heart 5 as the list ended without her name. Feeling 6, she walked home carrying her schoolbag full of homework.

    Arriving home, she started with math. She had always been a good math student, but now she was 7. She moved on to English and history, and was 8 to find that she didn't have any trouble with those subjects. Feeling better, she decided not to 9 math for the time being.

    The next day Jenna went to see Mrs. Biden about being on the school 10. Mrs. Biden wasn't as 11 as Jenna. “I'm sorry, but we have enough 12 for the newspaper already. Come back next year and we'll talk then.” Jenna smiled 13 and left. “Why is high school so 14?” she sighed.

    Later in 15 class, Jenna devoted herself to figuring out the problems that had given her so much 16. By the end of class, she understood how to get them right. As she gathered her books, Jenna decided she'd continue to try to 17 her new school. She wasn't sure if she'd succeed, but she knew she had to 18. High school was just as her mom had said: “You will feel like a small fish in a big pond 19 a big fish in a small pond. The challenge is to become the 20 fish you can be.”

    There are a number of ways to help improve your memory, so you shouldn't____sad.

    My first way is that if you want to remember something, you have to review it____.You may want to go over the material two days after you have____it, then a week later, then two weeks later, and then a month later. After a month you will find that you can remember the material.

    My second____is to use a colored pen to highlight(用颜色标出) the important parts on your book. This will help you in two ways. First, it will help you focus on the____parts when you learn the knowledge. It is always____than remembering everything.____this will make reviewing better. When you open your book, the color parts will show you the most important things immediately.

    Another good time for remembering information is in the morning because you have just ____the whole night and your brain is fresh and clear. So it's easy to remember the important information in the morning.