The topic of a piece of informational writing is the subject or focus.
The correct answer is "the subject or focus" of a piece of informational writing. The topic refers to what the writing is primarily about or what it focuses on. To determine the topic of a piece of informational writing, you can read the introduction or look for key phrases or sentences that clearly state the main subject or focus of the text. Additionally, headings and subheadings can often provide clues about the topic or main themes of the writing.