Down Syndrome Is Also Known as Trisomy 21 Because Individuals

Down syndrome is also known as trisomy 21 because individuals with Down syndrome ____.

A) have three distinct facial features by the twenty-first week of pregnancy
B) show three distinct temperament patterns by the twenty-first week of infancy
C) have a third chromosome on the twenty-first pair
D) have 21 genes on the third pair of chromosomes