Dennis Is Mentally Retarded

Multiple Choice

Dennis is mentally retarded. He has a flat nose, a protruding tongue, and upwardly slanted eyes. Which of the following statements is most likely to be true

A) Dennis has Down syndrome, caused by an extra 21^st chromosome.
B) Dennis has Down syndrome, caused by missing 21^st chromosome.
C) Dennis has Down syndrome, caused by maternal alcohol consumption.
D) Dennis has Down syndrome, caused by a lack of oxygen during birth.