If the ing form of a verb is used as the main verb of the predicate, the auxiliary must contain a form of blank

"first of all, how could they mistake a man for a sasquatch? " which best explains the purpose of this question (from review 2)? a) to illustrate how much the book uses humor b) to show how unbelievable parts of the story are c) to convince the reader that the novel is poorly written d) to highlight the differences between the characters in the novel