If Our Ancestors' Mental Abilities Increased in Parallel with an Increase

Multiple Choice

If our ancestors' mental abilities increased in parallel with an increase in brain size,why has the size of our brains not continued increasing?

A) the human skull is currently as large as the exoskeleton will support
B) factors other than the brain also determine human capabilities
C) although humans continue to evolve,language,memory,and attention are fully developed
D) this evolutionary mechanism is still at work; it just evolves more slowly than previously thought