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
Inversion is reversing the normal English word order of subject + verb. The everyday case is subject–auxiliary inversion for questions: Sam has read it → Has Sam read it?. The more advanced case is inversion after fronted negative or restrictive expressions: Rarely have I seen such dedication / Not only does she sing, she also writes.
The advanced kind is a hallmark of formal and literary English — used after openers like never, seldom, not until, only when, little did I know. Mastering it is a C1+ skill that signals careful, register-appropriate writing.
Interrogative sentence
An interrogative sentence asks a question. It ends with a question mark in writing and a rising intonation in speech: What do you want? / Are you feeling well? / Do you know who called? English forms questions by inverting the subject and an auxiliary verb (Are you ready?) or by adding do-support when no auxiliary is otherwise present (Do you know?).
Interrogatives split into yes/no questions (answerable with yes or no) and wh-questions (starting with what, where, when, who, why, how). It's one of the four sentence types alongside declaratives, imperatives, and exclamatives.
C1 | Advanced
C1 is the advanced level in the CEFR framework, sitting between B2 and C2. At C1 you stop translating in your head and start thinking in English — handling specialised articles outside your field, picking up implicit meaning, and writing structured arguments on complex topics.
Grammatically, C1 means natural use of inversion (Rarely have I seen…), mixed and advanced conditionals, subjunctive forms in formal contexts, and cleft sentences for emphasis. Most university programmes for non-native speakers and many professional certifications set C1 as their entry standard.
Difficulty: Hard
The Hard difficulty tag marks questions and challenges aimed at upper-intermediate to advanced learners — typically B2 and above. Expect interacting rules, edge cases, distractors that look right at first glance, and contexts where the surface meaning and the grammatical answer don't match.
Filter by Hard when you're past the basics and want material that genuinely tests your understanding. These questions catch the gaps your textbook didn't — register-sensitive choices, exception cases, mixed conditionals, the difference between would have been and had been.