What is the main function of the amniotic sac?

The main function of the amniotic sac is to surround the fetus with fluid, creating the amniotic cavity that cushions and protects the developing fetus throughout pregnancy. This fluid-filled environment helps to maintain a stable temperature and provides a buffer against external pressure, which is crucial for the fetus's development. The amniotic fluid also allows for movement, contributing to musculoskeletal development, and helps the fetus develop its lungs by facilitating breathing movements in the fluid.

In addition to these protective functions, the amniotic sac plays a role in the overall development of the fetus by allowing for the proper growth of the organs. Thus, the correct answer emphasizes the essential protective and supportive role the amniotic sac plays in fetal development.