实验时要让电阻R，两端的电压为2．5伏，电阻R1选用10欧的阻值时，滑动变阻器R接入电路的阻值应为____ 欧。

小明从甲地去乙地， $\frac{5}{3}$ 小时走了15千米，正好走了全程的 $\frac{3}{4}$ 。甲乙两地相距多少千米？

It's important for us to be healthy. But how can we keep healthy? First,you should eat fruit and vegetables three or four times a week. Then eat some tofu every day because it's good for people, both the young and the old. Milk is also necessary(必要的），especially for women. So you should have milk twice a day. It can help you to be strong. Next, doing more exercise is better. You can do morning exercises or evening exercises. After supper you should take a walk.