Down syndrome is also known as:

A) trisomy 12.
B) trisomy 13.
C) trisomy 18.
D) trisomy 21.

Trisomy 21

A genetic disorder caused by the presence of an extra 21st chromosome, also known as Down syndrome.

Trisomy 18

A genetic disorder caused by the presence of an extra 18th chromosome, leading to severe developmental and physical abnormalities.

Trisomy 13

Trisomy 13, also known as Patau syndrome, is a chromosomal condition associated with severe intellectual disability and physical abnormalities in many parts of the body.