题目内容：
It is natural that children are curious about the world around them.For example,they want toknow 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 parte of their bodies and in the smiles of their mothers.Then they become interested in the physical world around them:the plants,the animals,and the sky.Later,they
become interested in the things that people have made:wheels,bicycles,cars.And when they are nules,theirecuriosity econtinues,Sometimes huis curoeily leaulk to a curer in sciemnce.
Scientists spend their lives trying to find out about the world.Thoe who work with the earth
ociences study the earth,the ceans,and the akies.Other aeiemtins who touly loring lhinge work wilh the biological sciences.A thicd goup of scientistk audy the phywical wieces,e g phyuice,
chemistry.These scientists have already discovered a lot about our world.For example,they lell us why your heaurt beats fast when you run.They say thet when you are quiet,your heart normlly beats sixty-five or scventy-five times a minute.Your heart is a pump(泵）that pumps bloud to all parte 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 b
参考答案：