Question
Not sure what they mean by what are the conditions.
Answer
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What are the conditions" can mean two things, depending on the context. The question might refer to the shape that something is: the condition of a house, a car, a rental property, etc. Is it in good condition or bad condition? Does it need work or is it ready for use? The other option is that the question refers to an agreement or contract. I will loan you my vacation home on two conditions: that you pay me $500 and that you clean it when you leave. Those are "the conditions."
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Air is purified when contaminants are removed. There are lots of different techniques used to accomplish this and some purify the air more so than others.