在下列四个函数中，满足性质：“对于区间（1，2）上的任意$x_1,x_2(x_1\ne x_2)$.$\left|f\left(x_1\right)-f\left(x_2\right)\right|<\left|x_1-x_2\right|$恒成立”的只有（   ）

①向光性  ②向水性  ③向肥性  ④向地性．

阅读理解

     Basketball is still a young game. It's over a hundred years old. In the winter of 1891, a certain college was having some trouble with its boy students. The weather was bad and the students had to stay indoors. As they couldn't play outdoors, they were unhappy, and some even got into fights from time to time.
　　Some of the teachers, at the college asked Dr. Naismith to invent a game so that the students might have something to play with. It was not easy to invent such a game because it had to be played indoors, and the court (球场) was not very large.
　　Dr. Naismith thought for a few days and invented a kind of ball game. It was a fast, wonderful game with much moving and passing of the ball. It was played between two teams. To make a score , the ball had to be thrown into the basket ten feet(英尺) above the floor on the wall . At each end of the court there was such a basket. At first, Dr. Naismith wanted to throw the ball into a box. As he could not find boxes of the right size, he had to use fruit baskets instead. That is how the game got its name.