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

Input: Consider Input: Passage: Classification of Joints on the Basis of Function The functional classification divides joints into three categories: synarthroses, amphiarthroses, and diarthroses. A synarthrosis is a joint that is immovable. This includes sutures, gomphoses, and synchondroses. Amphiarthroses are joints that allow slight movement, including syndesmoses and symphyses. Diarthroses are joints that allow for free movement of the joint, as in synovial joints. Answer: synarthrosis

Output: What category of joints is immovable?

Input: Consider Input: Passage: The male gametophyte produces flagellated sperm that must swim to the egg formed by the female gametophyte. For this reason, sexual reproduction must happen in the presence of water. Therefore, nonvascular plants tend to live in moist environments. Though the life of a nonvascular seedless plant is a cycle, this can be considered the initial step in the life cycle. Answer: water

Output: When flagellated sperm must swim to the egg, sexual reproduction requires the presence of what substance?

Input: Consider Input: Passage: Most primates have opposable thumbs. An opposable thumb can be brought into opposition with the other fingers of the same hand. This allows the hand to grasp and hold things. Answer: primates
Output: Most members of what mammalian order possess opposable thumbs?