25 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 label right to left. "V/ii" means "the dominant OF ii": the chord after the slash is always the target being tonicized.
Look for the chromatic accidental. A note outside the key signature that resolves like a leading tone is the telltale sign of secondary function.
Only major/minor chords get tonicized. Rule out diminished triads (like vii°) as targets right away.
Read the explanations even when you're right. Each one reinforces a fact that often returns in a different form on the exam.