What does the term "supporting detail" mean in the context of a text?

The term "supporting detail" refers to a fact, example, or piece of information that adds strength and credibility to the controlling idea or main argument of a text. Supporting details serve to clarify, illustrate, or elaborate on the main point, providing evidence that the author's claims are valid and well-founded. By reinforcing the controlling idea, these details help to create a more persuasive and coherent argument.

In the context of the other options, a piece of information that contradicts the main idea does not serve to support but rather undermines the point being made. An unrelated anecdote lacks relevance and does not connect to the controlling idea, while a personal opinion from the reader also does not serve as support since it is subjective and not based on factual information. Thus, the choice that correctly defines a supporting detail is the one that describes it as a fact that reinforces the controlling idea.