The correct answer is turning down, as it is the gerund form of the verb "to turn down" and the verb "regret" requires something that functions as a noun.
Gerund
A gerund is the -ing form of a verb used as a noun — swimming, reading, being late. It can sit in any position a noun can: as the subject (Swimming is fun), as the object of a verb (I enjoy swimming), or as the complement of a preposition (She's good at swimming).
Gerunds matter because dozens of common English verbs and almost every preposition force you into the -ing form. Pick the wrong shape — I enjoy to swim, good at to swim — and the sentence sounds clearly off to a native speaker. Knowing which contexts demand a gerund (vs. an infinitive) is what makes verb patterns click.
Infinitive
The infinitive is the basic, unmarked form of a verb, used when no tense or subject agreement is needed. English has two flavours: the to-infinitive (to swim, to read) and the bare infinitive (swim, read). The to-infinitive follows verbs like want, decide, hope, plan (I want to swim); the bare infinitive follows modal verbs (I can swim) and certain causative verbs (Let him go).
Knowing which form to use after which verb is one of the trickiest distinctions in English — closely tied to the parallel choice of gerund (-ing form). I want to swim but I enjoy swimming aren't interchangeable.
Verb
A verb is a word that expresses an action, a state, or an occurrence — the engine of every English sentence. Most verbs have five forms: base (go), -s form (goes), past tense (went), past participle (gone), and -ing form (going). The verb be is the major exception with eight forms; modal verbs like can and must have fewer.
Verbs carry tense (when), aspect (how it unfolds), mood (the speaker's attitude), and voice (active vs passive). Mastering them is foundational — virtually every other grammar topic depends on getting verbs right.
Noun
A noun is a word that names something — a person, place, thing, idea, action, or quality. Nouns are one of the open word classes in English, alongside verbs, adjectives, and adverbs. They typically appear as the subject or object of a clause, after articles or adjectives, and as the head of a noun phrase.
Recognising nouns reliably is the foundation for nearly every other grammar topic — agreement, articles, plurals, possessives, and prepositions all depend on it. Get this right and the rest of English grammar starts to fall into place.
C2 | Proficiency
C2 is the highest level in the CEFR framework — the proficiency stage, where your English is nearly indistinguishable from a well-educated native speaker's. C2 users handle irony, understatement, and idiomatic range across any register, and they reformulate ideas under pressure without losing fluency.
C2 is less about learning new grammar and more about mastering the flexible, context-sensitive use of everything you already know. Most learners never reach C2 — and most don't need to. Knowing the level helps you set realistic goals: B2 or C1 is plenty for almost any practical purpose.
C1 | Advanced
C1 is the advanced level in the CEFR framework, sitting between B2 and C2. At C1 you stop translating in your head and start thinking in English — handling specialised articles outside your field, picking up implicit meaning, and writing structured arguments on complex topics.
Grammatically, C1 means natural use of inversion (Rarely have I seen…), mixed and advanced conditionals, subjunctive forms in formal contexts, and cleft sentences for emphasis. Most university programmes for non-native speakers and many professional certifications set C1 as their entry standard.
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.