With Regard to Fluid and Crystallized Intelligence, Research Has Concluded

With regard to fluid and crystallized intelligence, research has concluded that:

A) both fluid and crystallized intelligence increase or remain stable well into late adulthood.
B) crystallized intelligence improves or remains stable with age but fluid intelligence appears to decline in late adulthood.
C) both fluid and crystallized intelligence appear to decline with age.
D) fluid intelligence improves or remains stable with age but crystallized intelligence appears to decline in late adulthood.