Kendra was diagnosed with Down Syndrome when her mother was still pregnant with her. Which of the following is the scientific reasoning that she could teach to others to explain her disability?
A. This is a mutation on the X chromosome caused by environmental poisons.
B. It is a result of cystic fibrosis that she suffered from as an infant.
C. This is a mutation of the Y chromosome.
D. This is a genetic abnormality that happens because of the presence of three chromosome #21 instead of two.