In the sentence, " sweep the sidewalk after mowing," how is the word, mowing, a gerund used as the object of preposition ?
also, how is the same word a noun (because it is a gerund)?

Explanation:

It is the object of the preposition because the preposition is after and the prepositional phrase is "after mowing" therefore the object is mowing".Mowing is not a noun, a gerund is a verb that must've been a trick question.

the correct answer is the following.

one of the groups i belong to is the boy scouts. this is a problem-solving group because it has tasks that we need to solve in order to other people in different activities such as the rescue of lost pets, or elder people in need.

the other group i belong to is kids pro environment, and is an information-sharing group that tries to create conscience about the risks and problems that generate pollution in our cities. we share information to other students and parents on the importance of keep our communities clean and our skies clear.