An infinitive is a type of D. Verbal. It is one of the three types, besides gerunds and participles that are the other two types of verbals, whereas appositive is not a type of a verbal.
The topic sentence introduces the reader to what you will talk about.
B. They announce the main ideas of paragraphs
O. Henry's use of third-person narration in "After Twenty Years" means that the reader is able to make the crucial discovery of the cop's real identity at the same time as other characters in the...