Main Idea and Supporting Details
What to know
The main idea is the single point a paragraph or passage is built to communicate; supporting details are the examples, statistics, reasons, and illustrations that prove or explain it. Distinguish topic (a word or phrase: "urban gardening") from main idea (a sentence with a claim: "Urban gardens improve food access in low-income neighborhoods"). The main idea may be stated in a topic sentence or implied, requiring you to summarize. A passage's thesis is its main idea at the whole-text level.
Traps
Wrong answers are usually too broad, too narrow, or true but minor. A choice that repeats many words from the passage can still miss the point. Another trap is selecting a supporting detail as the main idea because it appears first or sounds impressive. Also watch for a sentence that is accurate but only covers one paragraph of a multi-paragraph passage.
Rule of thumb
Ask, "What is the whole passage mostly doing?" Then test each choice: does it cover all the paragraphs without adding information the passage never states?
Worked example: A three-paragraph passage describes a city's bike-lane expansion, cites a drop in collisions, and notes increased local business revenue. Choice A: "Bike lanes are painted green" (a detail). Choice B: "Cities should ban cars" (unsupported). Choice C: "The city's bike-lane program produced measurable safety and economic benefits" (correct-covers all paragraphs, no overreach).