The correct answers are Were aliens to land, If aliens were to land, and If aliens landed.
This is a second conditional sentence (unreal present/future), indicated by "would be required" in the main clause.
To express a highly unlikely hypothetical event, we can use "if + subject + simple past" (If aliens landed) or "if + subject + were to + base verb" (If aliens were to land).
For a more formal, literary tone, we can drop "if" and invert the subject and "were" (Were aliens to land).
"Had aliens landed" is incorrect because it is a third conditional form, which mismatches the main clause.
Conditional sentence
Second vs third conditional: second = unreal present/future (If I had money, I would buy it — but I don't have money now). Third = unreal past (If I had studied, I would have passed — but I didn't study). The most common confusion: using second when you mean third, making your timeline unclear.
A conditional sentence = if-clause + consequence clause. Five patterns (zero, 1st, 2nd, 3rd, mixed) each encode a specific time and probability.
Diagnostic: is the hypothetical about now or then? Now → second conditional. A past event that didn't happen → third conditional.
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.
Subjunctive mood
Subjunctive vs indicative: indicative states facts (He goes every day). Subjunctive marks unreality (I suggest he go; If I were you). The subjunctive drops the -s and insists on were — signalling "this isn't (or may not be) real." In informal speech it's disappearing, but formal/academic writing still expects it.
The subjunctive mood = hypothetical/counterfactual marker. Present subjunctive (base form after suggest/demand/insist that). Past subjunctive (were in unreal conditionals).
Diagnostic: is the clause about something unreal, demanded, or recommended (not yet true)? → subjunctive. Is it factual? → indicative.
Word order
English (SVO) vs other patterns: English relies on word ORDER to show who does what (Dog bites man ≠ Man bites dog). Inflected languages (Latin, Russian, German) use case endings and can scramble order freely. In English, changing order changes meaning or requires special constructions (inversion, cleft sentences).
Word order = how English marks grammatical relationships. SVO is the default; fixed adjective order; adverb placement varies by type.
Diagnostic: does your sentence sound "off" even though all word forms are correct? → probably a word order issue. Try moving the element back to default SVO position.
Verb mood
Mood vs tense: tense tells you WHEN (past/present/future). Mood tells you the speaker's ATTITUDE (fact/command/hypothetical). She goes (indicative + present) vs Go! (imperative) vs I wish she went (subjunctive + past form but present meaning). Mood and tense work independently.
Verb mood = attitude marking. Indicative (facts), imperative (commands), subjunctive (unreal), conditional (dependent). Each uses different verb forms or auxiliaries.
Diagnostic: is the speaker stating a fact? → indicative. Commanding? → imperative. Imagining something unreal? → subjunctive. Expressing what would happen under a condition? → conditional.
B2 | Upper Intermediate
B2 vs C1: B2 means effective communication on complex topics with some effort. C1 means effortless fluency with precise register control. If you can argue a point but still reach for words and make structural slips under pressure, you're B2.
B2 is the upper-intermediate CEFR level: mixed conditionals, complex passives, reported speech with backshift, participle clauses, and sustained written argument.
Diagnostic: does your writing read as "competent non-native" or "could be native"? The former → B2. The latter → 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.