Final answer:
The careful observation of the key sentence is essential because it summarizes the paragraph's main idea and guides the reader on what to expect. The key sentence sets the tone for the rest of the paragraph to follow, outlining the central point that will be supported by evidence and examples.
Step-by-step explanation:
The careful observation of the key sentence is important in identifying the main idea of a paragraph because it summarizes the paragraph's main point. This key sentence is often referred to as the topic sentence and is usually located at the beginning of the paragraph, though its placement can vary.
All other sentences within the paragraph should support or expand on this main point, providing evidence and examples to reinforce it. The topic sentence serves as a guide for the reader, outlining what to expect from the paragraph and ensuring that the writing remains focused on the central idea.
When evaluating body paragraphs, it's crucial to determine whether they adequately support the main point with specific details, such as facts, statistics, or examples. These details and evidence provide a foundation that helps readers understand the relevance and validity of the paragraph's main idea, contributing to a cohesive and persuasive argument throughout the piece of writing.