Given a scientific passage and an answer, generate a question for the given answer.
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Question: Passage: The lungs of mammals are unique in having alveoli. These are tiny, sac-like structures. Each alveolus is surrounded by a network of very small blood vessels (see Figure below ). Because there are millions of alveoli in each lung, they greatly increase the surface area for gas exchange between the lungs and bloodstream. Human lungs, for example, contain about 300 million alveoli. They give the lungs a total surface area for gas exchange of up to 90 square meters (968 square feet). That's about as much surface area as one side of a volleyball court!. Answer: alveoli

Answer: What in mammalian lungs, increases the surface area for gas exchange?

Question: Passage: Greenhouse gases include CO 2 , H 2 O, methane, O 3 , nitrous oxides (NO and NO 2 ), and chlorofluorocarbons (CFCs). All are a normal part of the atmosphere except CFCs. The table below shows how each greenhouse gas naturally enters the atmosphere ( Table below ). Answer: greenhouse gases

Answer: Co 2 , h 2 o, methane, o 3 , nitrous oxides (no and no 2 ), and chlorofluorocarbons (cfcs) are known as what type of gases?

Question: Passage: projectile motion: A form of motion where a particle (called a projectile) is thrown obliquely near the earth's surface, & it moves along a curved path under the action of gravity. The path followed by a projectile motion is called its trajectory. Projectile motion only occurs when there is one force applied at the beginning of the trajectory after which there is no interference apart from gravity. Answer: projectile

Answer:
What type of motion only occurs when there is one force applied at the beginning of the trajectory after which there is no interference apart from gravity?