Most people like bikes. Perhaps you ride a bike to school. Riding a bike can be great of fun.Do you know how to ride a bike safely?

    Careful boys and girls learn to ride their bikes well before they go out on the road.How can you tell whether you are a good rider?

    If you can ride a bike in a straight line,you can ride well .If you can't ,you should practice riding a in a safe place.

    To be safe on a bike, you need to use both hands and both feet. Keep your feet on the pedals(脚蹬)and your hands on the handle bars.

    You know that your bike is only for one person. It's not safe to carry anyone with you. Keep yourself safe when you ride on a bike.Watch where you are going all times.

唐朝具有繁荣和开放的特点，在世界上享有很高的声望，各国称中国人为“唐人”，许多国家至今还有“唐人街”。结合所学知识，回答下列问题：

椭圆$\frac{x^2}{a^2}+\frac{y^2}{b^2}=1\left(a>b>0\right)$的离心率为$e=\frac{1}{2}$，右焦点为$F\left(c,0\right)$，方程$a{x}^2+bx-c=0$的两个实根分别为$x_1$和$x_2$，则点$P\left(x_1,x_2\right)$（　）

    Has a doctor ever given you a note to take to the chemist for some medicine? Are you able to read the note easily? Some doctors write clearly , but most doctors do not. Chemists（药剂师） have more chances to read doctors'notes, but sometimes doctors write so badly that even the chemist can't read them.
   One day a lady wrote to a doctor inviting him to have dinner at her house. The doctor wrote an answer, but he didn't write clearly and the lady couldn't read it.
   “What shall I do?"she said to her husband, “I don't know whether he is coming or not. I don't want to give him a telephone call and say that I can't read his writing.”
   Her husband thought a moment, then he had an idea.
   “Thank you,"said his wife. “That's a very good idea.”
   She went to the chemist's shop and gave the doctor's note to the chemist. The chemist looked at it very carefully. Then he said politely, “Could you wait a moment, madam?" He went to the back of the shop. After a few minutes he returned carrying a large bottle. He gave the bottle to the lady and said, "Three times a day and one spoonful at a time.”

如图中，电荷的速度方向、磁场方向和电荷的受力方向之间关系正确的是（   ）