Which of the following explains mental growth most suitably?

Mental growth is best described as a uniform rise up to the middle teens followed by a gradual levelling off in the middle twenties.

Mental ability grows fastest in childhood and early adolescence, then slows as it nears its ceiling.

Saying it simply runs parallel to physical growth is inexact, since the two curves do not match in timing.

Calling it an erratic pattern is wrong, because mental growth follows a broadly regular, predictable curve.

Calling it not an erratic pattern is true but too vague, giving no description of the actual course.

Such growth curves underlie the concept of mental age used in early intelligence testing by Binet.