加热过氧化氢制氧气时，不放二氧化锰，其结果是（　　）

已知函数$f\left(x\right)=x^2-ax$的图像在点A(1,f(1))处的切线l与直线x十3y＋2＝0垂直，若数列$\left\{\frac{1}{f\left(n\right)}\right\}$的前n项和为$S_n$，则$S_{2013}$的值为 (    )

小华同学在“探究滑动摩擦力与压力大小关系”的实验中，他把物体用垂直于竖直墙壁的力F_压压紧在墙壁上，同时用竖直向上的力F匀速拉动物体向上运动，如图所示，保持其他条件不变的情况下，通过改变F_压来改变物体与墙壁之间压力的大小。经过多次实验测量F_压、F，记录了如下实验数据：

— What time do you usually      _________ every day?

—At seven o' clock. And then I will prepare breakfast for my son.

    David is from America. He and his family____(have) different plans for the coming holiday. David likes China very much and he____ (go) to Beijing last year. But he wants to know more about Chinese culture so he____ (visit) Beijing again. This time he is going to the Palace Museum. There____ (be) many interesting things about Chinese culture there. He____ (want) to take lots of photos of the things in the Palace Museum. He____ (show) them to his friends. David's father ____ (read) many books about Japanese history three months ago. He thought some things in Japan were interesting. He____ (take) a trip to Japan. David's mother didn't know where to go at first. At last she ____ (decide) to go to Singapore. She likes the climate (气候) there. What about David's sister? She ____ (stay) at home and do her homework.