How to keep healthy

    Everyone wants to be healthy,but do you know how to keep healthy? First, eating right food is very important. There is a lot of healthy food. It can make you strong. You can have more bananas,apples,tomatoes,cucumbers and so on, because fruits and vegetable are good for you.But you should not eat too much chocolate or fast food.They're not healthy food.Second,sports can also keep you healthy.Get up early and do some sports every day.You will be healthy and happy by doing so.

已知抛物线y=x²+bx+c与x轴交于A，B两点，与y轴交于点C，O是坐标原点，点A的坐标是（﹣1，0），点C的坐标是（0，﹣3）

(2)图甲的实验中，B组的作用是_____________ _________。