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
A conditional sentence describes one situation as depending on another. It pairs a condition clause (usually starting with if) with a consequence clause: If it rains, we'll stay in. The condition can refer to general truths, real future possibilities, hypothetical present situations, or unreal past situations — and each type uses a specific tense pattern.
English teaching groups these into zero, first, second, third, and mixed conditionals. Mastering them lets you talk about plans, regrets, hypotheticals, and warnings — territory you can't reach with simple present and past tenses alone.
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.
Subjunctive mood
The subjunctive mood is the verb form English uses for hypothetical, counterfactual, or formal-recommendation contexts. The two main patterns are: the present subjunctive in that-clauses after verbs of recommendation/insistence (I suggest that he go, It's essential that she be informed), and the past subjunctive were in counterfactual conditionals (If I were you).
Most subjunctive forms in modern English look identical to the indicative — the visible signs are the missing third-person -s (he go, not he goes) and were with first/third-person singular (if I were). Easy to miss; a strong marker of careful, formal English when used.
Word Order
Word order is the sequence in which words appear in a sentence. English is fundamentally an SVO language — subject, verb, object (Kate loves Mark). The order of adjectives, adverbs, and modifiers within a noun phrase also follows fixed patterns (a small red wooden box, not a wooden red small box).
In English, word order carries grammatical meaning — change the order and you change the sentence. The dog bit the man and The man bit the dog differ only in word order, but the meaning flips entirely.
Verb mood
Verb mood is the verb form that signals the speaker's attitude toward the action — whether it's a fact, a command, a hypothetical, or a recommendation. English has four main moods: indicative for statements and questions about facts (She works here), imperative for commands and instructions (Sit down!), subjunctive for hypothetical or formal-recommendation contexts (If I were you; I suggest he go), and conditional for would/could constructions (I would go).
Most English sentences are indicative — that's the default. The other three moods are smaller categories, but each marks a specific shift in meaning that can't be expressed any other way.
B2 | Upper Intermediate
B2 is the upper-intermediate level in the CEFR framework, sitting between B1 and C1. At B2 you can read editorials, follow most TED talks without subtitles, and hold extended conversations on abstract topics — including topics outside your everyday life.
Grammatically, B2 means flexible control of mixed conditionals, passive voice across tenses, reported speech with proper backshifting, and participle clauses. B2 is the standard target for university entrance exams (IELTS 5.5–6.5, TOEFL 87–109) and most skilled-migration thresholds — knowing whether you're there shapes your study plan.
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.