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

Q: Passage: Chemical cells are found in batteries. They produce voltage by means of chemical reactions. Chemical cells have two electrodes, which are strips of different materials, such as zinc and carbon. The electrodes are suspended in an electrolyte. This is a substance that contains free ions, which can carry electric current. The electrolyte may be either a paste, in which case the cell is called a dry cell, or a liquid, in which case the cell is called a wet cell. Flashlight batteries contain dry cells. Car batteries contain wet cells. Answer: chemical

A: Batteries produce voltage through what type of reaction?
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Q: Passage: Improving crops by selecting for certain genetic traits. The desired traits promote productivity. Recently, genetically engineered crops have been introduced. Answer: promotes productivity

A: What is the advantage of selecting for certain genetic traits for crops?
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Q: Passage: An underground layer of rock that is saturated with groundwater is called an aquifer . A diagram of an aquifer is pictured below ( Figure below ). Aquifers are generally found in porous rock, such as sandstone. Water infiltrates the aquifer from the surface. The water that enters the aquifer is called recharge . Answer: aquifer

A:
What is the name for an underground layer of rock that is saturated with groundwater?
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