Which of the following is true regarding brain development and aging?
a. blood flow is increased in the brain.
b. the brain uses more oxygen.
c. the brain becomes smaller and lighter.
d. the space between the brain and skull triples between 20 and 70 years of age.

a,c and d

Explanation:

- brain becomes smaller and lighter with age and although in absence of disease, it retains its structure and function.

- the brain shrinks, it pulls away from from the skull and the amount of amount of space between brain and skull doubles between 20 to 70 years of age.

- Blood flow reduces within the brain , which also uses less oxygen and glucose.

Hence, options a, c and d are correct.