阅读短文，下列问题

 B

      Bill sells Coca-Cola all over the world. Last week, he returned from the Middle East.   

       A friend asked, "How was your business with the Arabs?" "Too bad," Bill said in a sad voice. Then he explained, "When I got to the Middle East, I was very confident that I would have a good sale as Coca-Cola is well known around the world. However, I had a problem - I don't know how to speak Arabic. So I made some nice posters to help sell Coca-Cola. There are three pictures in each poster. In the first picture, a man is crawling (爬行) through ahot desert sand. He is terribly tired and thirsty. In the second one, the man is drinking our Coca-Cola with a big mouth. In the third one, he is smiling happily. Soon such posters were seen."

      "That's a good idea," said the friend. "Well, it should," Bill answered. "But I didn't know that Arabs usually read from right to left."

小东同学探究重力大小与质量的关系时，把不同质量的钩码挂在弹簧测力计下，分别测出它们所受的重力，并记录在下表中。根据数据归纳出物体所受重力大小与其质量的关系式为____ 。