Answer the following question given this paragraph: 

Attached to the placenta is the amniotic sac , an enclosed membrane that surrounds and protects the fetus (see Figure above ). It contains amniotic fluid, which consists of water and dissolved substances. The fluid allows the fetus to move freely until it grows to fill most of the available space. The fluid also cushions the fetus and helps protect it from injury.


Q: The amniotic sac is attached to what?


A:
placenta