=+4. Which of the following statements about the impact of aging is true?

a. During old age, many of the brain's neurons die.

b. If we live to be 90 or older, most of us will eventually become senile.

c. Older people become less susceptible to short-term illnesses.

d. Recognition memory-the ability to identify things previously experienced-declines with age.

e. Life satisfaction peaks in the 50s and then gradually declines after age 65.