Final answer:
Correct option C .introduction. The main idea should be included in the introduction of an informational text, where it serves as a roadmap for the reader and organizes the key points that will be discussed in the body paragraphs.
Step-by-step explanation:
The main idea of an informational text is essential and should be included prominently in the introduction of the piece. Planning the Main Points and Body Paragraphs involves clearly articulating your topic sentences, which anchor each paragraph. These sentences, generally positioned at the beginning, guide the reader through the text by precisely previewing what the subsequent paragraph will discuss.
The introduction serves as a roadmap, not only for the reader but also for you as a writer. It is where you should introduce your topic and outline the main arguments that you will cover in the body paragraphs. This organization helps maintain clarity and aids the reader in understanding the structure of your informational text.
In conclusion, the introductory paragraph of an informational text is crucial as it sets the stage and announces the key points that will be further explained in body paragraphs. It shall hence reflect upon the overarching main idea, which gives the reader a clear indication of the content they're about to digest.