Reading: Main Idea, Inference, and Purpose
What the questions actually ask
Reading items fall into a few predictable families: main idea and summary, detail retrieval, inference, vocabulary in context, author's purpose and tone, text structure, and evaluation of an argument. Name the family before you answer, because each one has a different rule for choosing between two plausible options.
Concepts you must control
Main idea is the claim the whole passage serves, not the topic it mentions most often. Supporting details prove the main idea; they never replace it. Inference answers must be forced by the text - a reasonable real-world guess the passage does not support is still wrong. For vocabulary, cover the word, predict a synonym from the sentence, then test that synonym in the sentence; the right answer preserves connotation (positive, negative, neutral), not just dictionary meaning. For purpose, ask what the author is doing (explaining, persuading, comparing, narrating) rather than what the passage is about. For argument, separate the claim from the evidence and check whether the evidence actually bears on the claim.
Traps
Wrong answers are often true statements that do not answer the question, or correct ideas contaminated by extreme wording ('always,' 'never,' 'proves'), or a detail promoted to main idea. Two-passage questions usually hinge on where the authors genuinely agree versus where they only seem to disagree.
Worked example
A passage says a program 'produced modest gains.' An answer choice calling the results 'a dramatic improvement' fails on connotation, even though both describe improvement. Rule of thumb: match the strength of the answer to the strength of the text.