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: Some nonmetals are very reactive, whereas others are not reactive at all. It depends on the number of electrons in their outer energy level. Answer: reactivity

Output: The number of electrons in the outer energy level determines what property of nonmetals?

Input: Consider Input: Passage: The Dust Bowl taught people that soil could be lost by plowing and growing crops. This led to the development of new ways of farming that help protect the soil. Some of the methods are described in Figure below . Answer: the dust bowl
Output: What historical event taught people that soil could be lost by plowing and growing crops and encouraged new methods to prevent erosion?