2．Why do we dream?

　　Given the fact that we spend around a third of our lives sleeping，shouldn’t we know everything about it？Unfortunately，scientists are still searching for a complete explanation of what happens when we sleep and why we dream.

　　Austrian psychologist Sigmund Freud believed dreams were the expressions of wishes that we can’t fulfill in our real lives.Others have wondered whether dreams are just random“noise” coming from a sleeping brain.

　　3．Could we someday live forever?

　　Apart from accidents，most people die because of diseases that can be treated and aging.And since many diseases，such as diabetes(糖尿病) and cancer，are diseases of aging，treating aging itself could be the key to extending our lives.

　　Our knowledge of what causes us to age—and what allows some animals to live longer than others—is expanding rapidly.And though we haven’t quite worked out all the details，we’ve worked out some pieces of the puzzles such as DNA damage and metabolism(新陈代谢) which are all leading to the invention of drugs that can slow down the aging process.

　　If we’re lucky enough to lengthen our lives，we might even get to see the day when all of these questions are answered.

　　1．The main point of the passage is

　　.

　　A．to inform people of the knowledge about the universe and nature

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