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

[EX Q]: Passage: Ocean water also absorbs gases from the atmosphere. The most important are oxygen and carbon dioxide. Oxygen is needed by living things in the oceans. Much of the carbon dioxide sinks to the bottom of the seas. Carbon dioxide is a major cause of global warming. By absorbing carbon dioxide, the oceans help control global warming. At least as long as the carbon dioxide stays in the seas. Answer: carbon dioxide
[EX A]: Oceans help control global warming by absorbing what?

[EX 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
[EX A]: Batteries produce voltage through what type of reaction?

[EX Q]: Passage: Water is needed by all known forms of life. Answer: water
[EX A]:
What is needed by all known forms of life?