Based on Longitudinal Studies, a Different Developmental Pattern for Intelligence

Based on longitudinal studies, a different developmental pattern for intelligence was revealed, which showed that

A) adults' intelligence peaked at age 18, and declined gradually thereafter.
B) adults tended to show increasing intelligence test scores until the mid-30s, then typically began to decline.
C) adults intelligence peaked in the mid-30s and then remained stable until the mid 50s.
D) adults' intelligence significantly slowed around their mid-30s.