According to the passage, children suffering from autism are unable to _______.

A．After five years of intensive treatment, Adam has completely recovered.
B．Mental retardation can result in autism.
C．Parents should know some key symptoms of autism so that they can spot the disorder.
D．Diagnosing autism in children is not difficult.

A．In the United States, rates of autism continue to skyrocket.
B．As many as 1 in 166 children born today is diagnosed with an autistic disorder.
C．Autism is the third most commonly diagnosed developmental disability in children.
D．The early diagnosis of autism is very important.