B
It is natural that children are curious about the world around them. For example, they want to know how their hearts beat. They want to know why the ocean water tastes salty.
As children grow up, they become curious about different kinds of things. When they are babies, they are interested in the parts of their bodies and in the smiles of their mothers. They become interested in the physical world around them: the plants, the animals, the sky. Later, they become interested in the things that people have made: wheels, bicycles, cars. And when they are adults, their curiosity continues. Sometimes this curiosity leads to a career (生涯、职业) in science.
Scientists spend their lives trying to find out about the world．Those who work with the earth sciences study the earth, the oceans, and the skies. Other scientists who study living things work with the biological sciences. A third group of scientists study the physical sciences, e. g. physics, chemistry .
These scientists have already discovered a lot about our world．For example, they tell us why your heart beats fast when you run. They say that when you are quiet, your heart normally beats sixty-five or seventy-five times a minute. Your heart is a pump (泵) that pumps blood to all parts of the body. The blood carries oxygen and nutrition. When you run, your muscles work very hard and use the nutrition that the blood carries to them. The muscles need oxygen, too . So your brain sends a signal to the heart. The signal means that the muscles need more nutrition and oxygen. Then the heart beats fast and sends blood quickly to the muscles. It may beat 90 to 140 times a minute.
Of course, scientists cannot answer all of our questions. If we ask, “Why does the ocean water taste salty” scientists will say that the salt comes from rocks. When a rock gets very hot or very cold, it cracks. Rain falls into cracks. The rain then carries the salt into the earth and into the rivers. The rivers carry the salt into the ocean. But then we ask , “What happens to the salt in the ocean? The ocean does not get saltier every year.” Scientists are not sure about the answer to this question.
We know a lot about our world, but there are still many answers that we do not have, and we are curious.
45．According to the passage, which of the following statements is true?
A．People are curious in the same way.
B．People in different countries are interested in different things.
C．Men and women are curious about different things.
D．People of different ages are interested in different things
46．Scientists who work with the biological sciences study____.
A．the earth , the oceans and the sky B．man-made things
C．plants and animals D．ocean water
47．When you run, your muscles need ____.
A．more nutrition and oxygen B．more signals C．more salt D．water
48．A rock cracks _____.
A．in wet regions B．in dry regions
C．at very high or very low temperatures D．when salty water falls in