Will they have finished dinner before we get there?
You asking a question about a future event, so you use the future perfect: will have finished. And because it is a question, the first auxiliary verb (will) and the subject (they) are inverted, the rest of the sentence stays the same.
Inversion
Question inversion vs emphatic inversion: question inversion is basic grammar (Is she ready?) — every learner uses it. Emphatic inversion (Never have I seen…, Not only does she…) is a C1+ rhetorical tool for formal writing and speeches. Same mechanism, different register.
Inversion swaps subject + auxiliary order. Triggered by: questions, fronted negatives (Never, Rarely, Not only), and conditional if-deletion (Had I known…).
Diagnostic: is a negative/restrictive word at the front of a declarative sentence? → inversion required. Is it a question? → inversion is automatic.
Interrogative sentence or clause
Interrogative vs declarative: declarative = subject before verb (She is ready.). Interrogative = auxiliary before subject (Is she ready?). The structural difference is inversion — swap subject and auxiliary to turn a statement into a question.
An interrogative sentence asks a question: yes/no (Is he…?) or wh- (What is…?). Formed by inversion or do-support, ending with a question mark.
Diagnostic: is the auxiliary/do before the subject? → interrogative. Is the subject first? → declarative (even with rising intonation).
C1 | Advanced
C1 vs C2: C1 means fluent and flexible use with occasional gaps in very unfamiliar domains. C2 means native-like command of idiom, irony, and register across any subject. If you can handle advanced grammar but still miss cultural nuance or very rare idioms, you're C1.
C1 is the advanced CEFR level: inversion, cleft sentences, subjunctive mood, advanced conditionals, and precise register control in professional and academic contexts.
Diagnostic: can you write persuasively in different registers and catch subtle irony? Consistently → C2. Sometimes → C1.
Hard
Hard vs Medium: Medium tests one rule with realistic distractors. Hard tests interacting rules, edge cases, or context-dependent answers where multiple options seem correct until you think deeply. If you're scoring 80%+ on Medium, try Hard to find your real gaps.
The Hard tag filters for B2+ challenges with layered difficulty: rule interactions, subtle distractors, and contexts that demand genuine grammatical reasoning.
Diagnostic: if Hard questions feel impossible, drop to Medium and master the individual rules first. Hard assumes you already know each rule — it tests whether you can apply them together.