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)?

When conducting research online, the key word or key phrase you type into a search engine should be a. as general as possible to include all possible results. b. unchanging from search to search so that you get consistent results. c. as clearly defined as possible so in order to narrow your search. d. flexible and applicable to a variety of topics.