In Binet's Measure of Intelligence, a Subnormal Child Was a Child

In Binet's measure of intelligence, a subnormal child was a child that:

A) had a reaction time of less than 1.5 meters a second.
B) had a reaction time of more than 1.5 meters a second.
C) successfully solved problems their parents gave them but not their school teacher.
D) could not solve the problems solved by children of the same age.