The planetary nebulae have nothing to do with planets.
Why it is true
Planetary nebulae are clouds of gas and dust ejected by dying stars. The name arose in the 18th century when astronomers mistook them for planets due to their round shape.
Source: NASA
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This is the reading side of the site, so the answer is in the sentence above — that is the whole point of it. Test yourself works the other way round: the question comes on its own, and the fact and the explanation only appear once you have answered.