Approximately ____ percent of intellectual disability cases can be attributed to known biological abnormalities.
a. 5
b. 20
c. 50
d. 80
Question 2
In 1866, what did the British physician Langdon Down describe for the first time?
a. characteristics of autism
b. a subgroup of intellectual disabilities
c. the case of the wild boy of Aveyron
d. the condition of pervasive developmental disorder