Article

✅ an hour — ❌ a hour (vowel sound → an)
✅ a university — ❌ an university (consonant sound /j/ → a)
✅ I love coffee — ❌ I love the coffee (generic uncountable → zero article)
✅ the sun — ❌ a sun (unique referent → the)

Articles (a/an, the, and the zero article) signal whether a noun is specific or general. A/an introduces something new; the points to something already known or unique.

Pattern: a/an = "one of many, first mention." The = "you know which one." Zero article = generic or uncountable.

Hard

Had she not intervened, the situation would have escalated. — inverted conditional
All distractors are grammatically plausible in other contexts
Multiple rules interact (e.g., tense + aspect + modality)
Context determines the answer — no single "rule" is enough

Hard marks upper-intermediate to advanced challenges: B2+, interacting rules, edge cases, plausible distractors, and contexts where pattern-matching fails.

Use "Hard" when Easy/Medium feel trivial and you want to test whether you actually understand a rule versus just recognising surface patterns.