34 multiple-choice questions in College Board exam style. Each has four choices and a full explanation of why each option is right or wrong.
Read the question carefully before looking at the choices. Many APES questions have answers that look almost identical; small wording differences matter.
Distinguish ground-level ozone from stratospheric ozone. This is one of the most commonly confused pairs in the entire course.
Know which pollutants are primary vs. secondary. This distinction shows up constantly in Unit 7 questions.
Read the explanations even when you got it right. Each one teaches a small fact that often returns in a different form on the exam.