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.

①《南京条约》      ②《马关条约》       ③与英、法签订的《北京条约》

在平面直角坐标系中，把点P（4，5）绕原点旋转90°得到点P₁，则点P₁的坐标是（　　）