Given a scientific passage and an answer, generate a question for the given answer.

[Q]: Passage: Mollusks reproduce sexually. Most species have separate male and female sexes. Gametes are released into the mantle cavity. Fertilization may be internal or external, depending on the species. Fertilized eggs develop into larvae. There may be one or more larval stages. Each one is different from the adult stage. Mollusks have a unique larval form called a trochophore . It is a tiny organism with cilia for swimming. Answer: trochophore
[A]: What is the unique larval form of mollusks called?

[Q]: Passage: Heat waves have increased in frequency and duration in recent years. The summer 2011 North American heat wave brought record temperatures across the Midwestern and Eastern United States. Many states and localities broke records for temperature and for the most days above 100 o F. Answer: cell membrane
[A]: What are all cells surrounded by?

[Q]: Passage: Within seconds of birth, the umbilical cord is cut. Without this connection to the placenta, the baby can't exchange gases, so carbon dioxide quickly builds up in the baby's blood. This stimulates the baby's brain to trigger breathing, and the newborn takes her first breath. Answer: umbilical cord
[A]:
What structure connects the fetus to the placenta, allowing the exchange of gases?