Definition: Given a scientific passage and an answer, generate a question for the given answer.
Input: Passage: The fetus is connected to the placenta through the umbilical cord. This is a long tube that contains two arteries and a vein. Blood from the fetus enters the placenta through the umbilical arteries. It exchanges gases and other substances with the mother's blood. Then it travels back to the fetus through the umbilical vein. Answer: placenta
Output:
The umbilical cord connects the fetus to what structure?