Given a scientific passage and an answer, generate a question for the given answer.
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Question: Passage: Hinge Joint. The knee joint is a hinge joint. Like a door hinge, a hinge joint allows backward and forward movement. Answer: hinge joint

Answer: What type of joint is the knee joint?

Question: Passage: Renewable resources are natural resources that can be replaced in a relatively short period of time or are virtually limitless in supply. Renewable energy resources include sunlight, moving water, wind, biomass, and geothermal energy. Each of these energy resources is described in Table below . Resources such as sunlight and wind are limitless in supply, so they will never run out. Besides their availability, renewable energy resources also have the advantage of producing little if any pollution and not contributing to global warming. The technology needed to gather energy from renewable resources is currently expensive to install, but most of the resources themselves are free for the taking. Answer: renewable resources

Answer: What are natural resources which can be replaced in a relatively short period called?

Question: Passage: Crystalline solids are generally classified according the nature of the forces that hold its particles together. These forces are primarily responsible for the physical properties exhibited by the bulk solids. The following sections provide descriptions of the major types of crystalline solids: ionic, metallic, covalent network, and molecular. Answer: crystalline solids

Answer:
What kind of solids are generally classified by the forces that hold their particles together and include ionic, metallic, covalent network, and molecular types?