Which one of the sentences is a run-on sentence? Fads and trends that are popular for a while but soon fade.
People of all ages and sizes often wear clothing that is popular, whether the style is flattering or not.
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Sometimes fads take the form of an activity rather than an item, aerobic exercise is a good example.
Children's toys are good examples of how fads often become crazes and then quickly lose buyer appeal.
None of these are run-on sentences.