题干

对任意x,y∈R,函数f(x)都满足f(x+y)=f(x)+f(y)+2恒成立,则f(5)+f(﹣5)等于(   )

A:0

B:﹣4

C:﹣2

D:2

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B

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    Are These the Best Years of Your Life?

    The ups and downs of life may seem to have no predictable plan. But scientists now know there are very clear life patterns that almost all people share. Even if you have passed some of your best years, you still have other good years to come.____

    When are you smartest? From 18 to 25, according to I. Q. scores; but you are wiser and more experienced with increasing age. You're sharpest in your 20's; around 30, mental abilities begin to decline, particularly your ability to do maths.____ Your vocabulary at age 45, for example, is three times as great as when you graduated from college. At 60, your brain possesses almost four times as much information as it did at age 21.

    ____You have the best physical sense of yourself from 15 to 24, when you feel energetic all the time. The best professional sense seems from 40 to 49. Before age 24, we believe that our happiest years are yet to come. Over 30, we believe that they're behind us. A National Health Survey agrees: After age 30, we “become more realistic and do not view happiness as a goal in itself. If we keep our health, achieve professional and emotional goals, then happiness, we feel, will follow.”

    ____Generally between 30 to 39, but the peak(顶峰)varies with different professions. Mozart wrote a symphony by age eight, and Mendelssohn composed his best-known work, A Midsummer Night's dream, at 17, but most of the great music was written by men between 33 and 39. Though the peak in most fields comes early—most Nobel Prize winners did their top research in their late 20's and 30's, creative people continue to produce quality work throughout their lives.____

A. When are you happiest?

B. When are you most creative?

C. But your ability to complete other tasks climbs.

D. The above gives you an accurate figure.

E. Certain good years seem to come later in life.

F. For people who are creative, there is no upper age limit.

G. The human life journey cannot be charted by a clear life pattern.