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

Q: Passage: Bone marrow is a soft connective tissue that produces blood cells. It is found inside the pores of spongy bone. Answer: bone marrow

A: What is found inside the pores of spongy bone?
****
Q: Passage: Density is defined as the mass of an object divided by its volume. Propose a unit of density in terms of the fundamental SI units. Answer: volume

A: Density is defined as the mass of an object divided by its what?
****
Q: Passage: Giant tube worms are found at hydrothermal vents. They get food from the chemosynthetic bacteria that live within them. The bacteria provide food; the worms provide shelter. Answer: hydrothermal

A:
What type of vents are giant tube worms found at?
****