Final answer:
When MS-AFP, hCG, inhibin A, and estriol levels are low, it indicates a higher risk for Down syndrome, a genetic disorder caused by an extra copy of chromosome 21.
Step-by-step explanation:
The answer to the question is b) Down syndrome. When MS-AFP, hCG, inhibin A, and estriol levels are low, it indicates a higher risk for Down syndrome. Down syndrome is a genetic disorder caused by an extra copy of chromosome 21. It is characterized by certain physical and intellectual impairments.