"have failed" is the correct option because it is in the present perfect tense, which is used to indicate that an action has been completed in the past but has a connection to the present. "Fail" is in the present simple, which is not appropriate in this context because the action is completed. "Had failed" is in the past perfect, which is used to indicate that an action was completed before another action in the past. This option doesn't match the context of the sentence, as there's no other action in the past that this is being compared to. "Was failing" is in the past continuous, which is used to indicate that an action was in progress at a specific time in the past. But this option doesn't match the context of the sentence, as the speaker is describing the result, not the progress of the action.
Present tense
- I work here. — simple present (habit/permanent)
- I am working now. — present progressive (happening right now)
- I have lived here for 10 years. — present perfect (started past, still true)
- I have been waiting for an hour. — present perfect progressive (duration up to now)
Four present tense forms: simple (habits/facts), progressive (now/temporary), perfect (past → present relevance), perfect progressive (ongoing duration). Each encodes a different relationship between the action and the present moment.
Trap: "I am living here for 10 years" ❌ — started in the past + still true = present PERFECT (have lived/have been living), not progressive.
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).
Clause
- I missed the bus. — ✅ independent clause (stands alone)
- Because I overslept. — ❌ fragment (dependent clause, can't stand alone)
- Because I overslept, I missed the bus. — ✅ dependent + independent = complete sentence
- I missed the bus, and I was late. — ✅ two independent clauses joined by and
A clause is a unit built around a verb with a subject. Independent = can stand alone. Dependent = needs an independent clause to complete it.
Test: does the group of words have a subject + verb AND can it be a sentence on its own? Yes → independent clause. Has a subject + verb but feels incomplete → dependent clause.
Adverb
- ✅ She sings beautifully — ❌ She sings beautiful
- ✅ He drives carefully — ❌ He drives careful
- ✅ They arrived late — ✅ a late train (same form, both roles)
- ✅ She works hard — ❌ She works hardly (different meaning!)
The -ly words are adverbs — they modify verbs, adjectives, or other adverbs, telling you how, when, where, or to what degree.
Pattern: most adjectives become adverbs by adding -ly, but watch the exceptions — fast, hard, late, well — that keep the same shape or change meaning entirely.
C1 | Advanced
- ✅ Not only did she finish early, but she also helped others. — inversion for emphasis
- ✅ It is the process that matters, not the result. — cleft sentence
- ✅ I insist that he be present. — formal subjunctive
- ✅ Were I to disagree, I would say so. — inverted conditional
These are C1 structures — the CEFR advanced level. At C1 you control inversion, cleft sentences, subjunctive forms, and register-switching fluently across formal and informal contexts.
Marker: if you can restructure a sentence for rhetorical effect without hesitation, you're C1.
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.