Six-Year-Old John Scores 50 on the Stanford-Binet Test

Multiple Choice

Six-year-old John scores 50 on the Stanford-Binet test. Which of the following is also necessary to classify him as "mentally retarded"?

A) evidence of chromosomal abnormality
B) proof that he does not have phenylketonuria
C) inability to perform daily tasks needed to function independently
D) the probability that his IQ will decrease as he ages