Complete the museum curator's dramatic press release about the missing gemstone. Choose the phrase that correctly uses a double passive construction to show a current belief about a past action.
The cursed diamond _______________ by a notorious syndicate of jewel thieves before the alarm even sounded.
The correct answer is is believed to have been stolen.
This sentence requires a double passive. The first passive (is believed) shows that this is the current consensus of the authorities. The second passive is a perfect passive infinitive (to have been stolen), which indicates that the action happened to the diamond in the past.
The other options incorrectly use active verbs, which would imply the diamond itself has beliefs or was out stealing things!
Passive voice
- ✅ The meal was cooked by the chef. — passive (action matters)
- ✅ Mistakes were made. — passive, agent hidden (evasive)
- ✅ Active: The chef cooked the meal. — stronger, clearer
- ❌ The report was being been written. — malformed passive
The passive = be + past participle. Object becomes subject. Use it when the doer is unknown, irrelevant, or obvious. Avoid when it hides responsibility or weakens prose.
Formula: find the active object → make it the subject → use be (matching tense) + past participle → optionally add by + agent.
Perfect tense
- ✅ I have lived here for ten years. — present perfect (started past, still true)
- ❌ I live here for ten years. — wrong (simple present can't bridge past→now)
- ✅ She had finished before I arrived. — past perfect (earlier past)
- ✅ They will have left by noon. — future perfect (completed before future point)
The perfect = have + past participle. Connects an action to a reference point in time. Present perfect bridges past→now. Past perfect marks "earlier past." Future perfect marks "done before a future deadline."
Rule: if the action started in the past and is still relevant now → present perfect (have done). If two past events and you need the earlier one → past perfect (had done).
Infinitive
- ✅ I want to go. — to-infinitive after want
- ✅ She can swim. — bare infinitive after modal
- ✅ Let me help. — bare infinitive after let
- ❌ I enjoy to read. — wrong (enjoy takes gerund, not infinitive)
The infinitive has two forms: to-infinitive (to go) after verbs like want, decide, plan, hope; bare infinitive (go) after modals and causatives (let, make, help).
Rule: after want, need, decide, plan, hope, expect, agree, refuse → to-infinitive. After can, will, must, let, make → bare infinitive. After enjoy, avoid, finish → gerund, NOT infinitive.
Verb
- walk → walk / walks / walked / walked / walking (5 forms, regular)
- go → go / goes / went / gone / going (5 forms, irregular)
- be → am/is/are/was/were/be/being/been (8 forms)
- can → can / could (modal: only 2 forms, no -s, no -ing)
A verb is the one word class every English sentence requires. Carries tense (when), aspect (duration), mood (attitude), and voice (active/passive). Regular verbs add -ed; ~200 irregular verbs have unpredictable past forms.
Key insight: fix your verbs and most grammar problems disappear. Wrong tense, wrong agreement, wrong form — verb errors account for the majority of grammatical mistakes.
C2 | Proficiency
- ✅ His was a pyrrhic victory, if ever there was one. — literary allusion + inversion
- ✅ She'd have been none the wiser had he not let slip. — inverted conditional + idiom
- ✅ The proposal, laudable though it may be, fails on pragmatic grounds. — formal concession
- ✅ "Nice weather," he deadpanned, eyeing the hailstones. — irony + narrative register
These are C2 patterns — the highest CEFR level. At C2 you handle literary allusion, irony, any register, and complex written argument with native-like precision across all subjects.
Marker: if your English is indistinguishable from an educated native speaker's across registers, you're C2.
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.