The correct answers are have, did, and was not.
Explanation:
When using ellipsis in coordination, the auxiliary verb in the second clause must logically match the tense and structure of the first clause.
- have: The first clause uses the present perfect (has confessed). The second clause uses inversion with "so" (so have his accomplices). Because "accomplices" is plural, we use have.
- did: The first clause is in the simple past (didn't suspect). The second clause uses inversion with "nor". The matching past tense auxiliary is did (nor did the security chief [suspect]).
- was not: The first clause uses the past simple passive (were recovered). The singular subject "ruby" requires the singular passive auxiliary was not (was not [recovered]).
Auxiliary verb
If you've ever wondered why English asks Do you know? instead of Know you?, or how a single sentence can carry tense, aspect, AND voice (has been being cleaned), you've felt the work of auxiliary verbs. They're tiny words that quietly carry most of English's grammatical machinery — get them wrong and questions, negatives, and tenses all fall apart.
An auxiliary verb combines with a main verb to add grammatical meaning. The English auxiliaries are be, have, do, and the modal verbs (can, will, should…). They handle questions (Do you?), negation (don't), tense and aspect (has gone, is going), and passive voice (was eaten).
Inversion
If you've ever read Rarely have I seen such talent in a book or speech and wondered why the verb came before the subject — you've met inversion's literary form. It's the same machinery English uses for questions (Has Sam read it?) but applied to declarative sentences for emphasis. Mastering it is the difference between flat formal writing and prose that lands.
Inversion swaps the normal subject + verb order. The basic case is questions: Has Sam read it?. The advanced case is fronted negatives and restrictives: Rarely have I seen such dedication; Not only does she sing, she also writes. The latter is a C1+ feature.
Coordination
If you've ever stared at a list and not known whether to use and or a comma, or whether the items in your list need to be parallel — you've hit the rules of coordination. Get them right and your sentences flow; miss them and your reader stumbles over awkward constructions like I like reading, swim, and to cook.
Coordination links two or more elements of equal grammatical weight using a coordinating conjunction — and, or, but. The linked items must be the same kind of thing: noun + noun, clause + clause, verb phrase + verb phrase. Mismatched items make the sentence sound clearly off.
Verb tense
If you've ever frozen mid-sentence wondering whether to say I worked or I have worked, I had been doing or I was doing — you've felt the weight of English's tense system. Twelve forms, each with a specific job, and the wrong choice subtly misrepresents your meaning. Mastering tenses is the longest single project in English grammar, but it's also the one with the biggest payoff.
Verb tense signals when an action happens. English has three time references (past, present, future) combined with three aspects (simple, progressive, perfect), giving twelve standard forms. Each carries a specific meaning beyond just timing.
Passive voice
If your writing has been called "weak" or "evasive" — Mistakes were made, It was decided that... — you've hit the passive voice's main pitfall. Used deliberately, the passive is precise and useful: it foregrounds the action when the doer doesn't matter. Used by default, it makes prose feel like nobody's responsible for anything.
The passive voice is formed with be + past participle and turns the object into the subject: The chef cooked the meal → The meal was cooked (by the chef). Useful when the action matters more than the doer; overused, it makes writing feel evasive.
C1 | Advanced
If you've ever sat through a lecture in English, written a complaint letter, or argued a point in a meeting and come out feeling actually understood — not just tolerated — you've felt what C1 looks like. The level matters because it's where most universities, certifications, and skilled-work environments draw their language line.
C1 is the advanced level in the CEFR framework, demanding fluent and flexible language: inversion for emphasis, mixed and advanced conditionals, formal subjunctive, cleft sentences, and complex nominal phrases — all used appropriately across registers.
Difficulty: Hard
If easy and medium questions are clicking but you still feel exposed in real conversation or formal writing, you've outgrown the basics. Hard material is where the gaps you didn't know you had show up: the distractor that "sounds right", the rule that interacts with another rule, the case where context changes the answer. It's where genuine fluency is built.
The Hard difficulty tag marks upper-intermediate to advanced challenges — typically B2 and above. Interacting rules, edge cases, plausible distractors, and contexts that require genuine understanding rather than surface pattern-matching.