One day when Isaac Newton was reading a book under an apple tree on the farm, an apple fell down and hit him on the head. For most people that would be the end of the story, but not for Newton. Why did the apple fall out of the tree? Does everything fall? What makes things fall? Can anything stop things from falling? Are the sun, moon, and stars falling? Why don’t they ever hit the ground?
So many questions. Newton spent many years answering these questions by thinking and doing experiments. He made up the law of gravity. According to this law everything pulls everything else to itself by a force called gravity. How strong that force is depends on how heavy the things are and how close together.
Newton’s law of gravity not only explained how things fall on earth, but now planets move around the sun and how moons move around planets. A friend of his, Edmund Halley, decided to try Newton’s theory on comets. People had been studying comets for hundreds of years without figuring them out, so he decided to study their reports and compare them to Newton’s theory.
Up till then people had thought that comets just came and went, and that nobody could know when or why. But Newton’s law of gravity gave rules that Halley could use to study the records of comets. He found some reports of a big bright comet that he was sure was the same one, coming back every 75 years. He predicted when it would come back next.
If anybody still didn’t believe Newton, then the appearance of Halley’s Comet just when Halley had predicted it using Newton’s ideas was enough to convince them. Halley’s Comet has come a few times since then, always right on schedule. You’ll be able to see it on its next trip near the sun and earth when you’re old enough to be a grandparent.
71.The passage starts with a story _____________.
A.because it was such a funny one
B.because Newton liked to eat apples
C.to show how much Newton liked reading
D/to show what started Newton’s discovering gravity
72.According to the author, Newton was especially different from others in that ____________.
A.he liked reading under apple trees
B.he liked to find out how things worked
C.he was very quiet and patient
D.he was so much interested in science
73.Newton’s law of gravity can tell us that _____________.
A.gravity has no relationship with the weight of things.\
B.how things fall on earth
C.it is not of help to the study of comets
D.it can explain everything in the world
74.The underlined word “ convince” in the last paragraph probably means “______________”
A. make… believe B. make… doubt
C. make… understand D. make… interested
75. Which of the following is TRUE about Edmund Halley?
A. He discovered a big bright comet.
B. He helped Newton to create his theory.
C. He predicted when the same comet would come back.
D. He studied the same comet for 75 years.