Definition: Given a scientific passage and an answer, generate a question for the given answer.
Input: Passage: Bones consist of four different types of tissue: periosteum, compact bone, spongy bone, and bone marrow. Ossification gradually changes the cartilage skeleton of the fetus to the bony skeleton of the adult. Answer: periosteum
Output:
Bones consist of four types of tissue, compact bone, spongy bone, bone marrow, and what?