Explanation:In an essay, article, or book, an introduction is a beginning section which states the purpose and goals of the following writing. This is generally followed by the body and conclusion. The introduction typically describes the scope of the document and gives the brief explanation or summary of the document.
An introduction refers to a beginning — maybe presenting someone new to a group, or inserting a new idea into a project. ... The noun introduction comes from the Latin verb introducere, meaning "to lead in." This “leading in” might be the formal introduction of a speaker, or the speaker's own introduction to his remarks.
The answer is D because it's unclear who the pronoun in that sentence ("his") is referring to - is it Mario or Mario's little brother that it's talking about?