题目内容：
Passage ThreeMy formula for staying young is simple: concentrate on the part of you that's young and growing—your brain. Keep your mind awake and you'll stay young all over. These are exciting times. Take an interest in the world around you, and make a point of learning at least one new thing every day.
Regardless of your age, it's not too late to make your life more interesting. I know a housewife with no previous knowledge who made herself into an outstanding industrial designer; I know a retired electrical engineer who has become a highly paid ceramic artist.
Get over the notion that you are ever too old to go back to school. I know a man who entered medical college at 70. He got his degree with honors and became an eminent physician. Another man went to law school 71 and is now an active lawyer.
In spite of years, staying young is easy for those who live in the future. You can do it if you care enough to try. Keep your mind awake and active; that's the only youth elixir guaranteed to work.
The statement that our brain remains young and growing regardless of age is ________. A．an impossibility
B．a scientific fact
C．a supposition
D．a ridiculous conclusion
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