The correct answers are Many a dusty scroll has been deciphered in this laboratory. and A great number of dusty scrolls have been deciphered in this laboratory.
"Many a" is an advanced, slightly formal construction that takes a singular countable noun and a singular verb (e.g., Many a scroll has...).
"A great number of" correctly pairs with plural countable nouns and plural verbs (e.g., A great number of scrolls have...).
"Amount" is used for uncountable nouns (like water or courage), not countable nouns like scrolls.
Determiner
Determiner vs adjective: both appear before a noun, but determiners specify which/how many while adjectives describe what kind. Determiners come first: the big cat (✅) vs big the cat (❌). You can stack adjectives (big fluffy cat) but generally only one determiner per noun.
A determiner is a function slot before a noun filled by articles, demonstratives, possessives, or quantifiers.
Diagnostic: does the word tell you which one or how many rather than what kind? → determiner. Does it describe a quality? → adjective.
Countable and uncountable
Countable vs uncountable: countable nouns can be numbered and pluralised (one book, two books). Uncountable nouns can't (information, not informations). The distinction determines your choice of article, quantifier (much/many, few/little), and whether the noun can be plural.
Countable = takes a/an, has a plural, uses many/few. Uncountable = no a/an, no plural, uses much/little. Some nouns are both depending on meaning (coffee = the substance vs a coffee = a cup).
Diagnostic: can you say one ___, two ___s? Yes → countable. No → uncountable (use a unit phrase: a piece of, a bit of).
Subject
Subject vs object: the subject does or is; the object receives. She (subject) hit him (object). In English, position decides: subject comes before the verb, object after. Unlike inflected languages, English rarely marks subjects with case (exception: pronouns — I vs me).
The subject = who/what the sentence is about. Controls verb agreement. Usually a noun/pronoun before the verb.
Diagnostic: ask "who or what [verb]s?" The answer is the subject. The list of items is wrong — what is wrong? The list. That's your subject.
Noun
Noun vs verb: the two core word classes. Nouns name things; verbs describe actions/states. Many English words can be both (run, play, cook, work) — only the sentence slot tells you which role it's playing. The run was exhausting (noun) vs I run every day (verb).
A noun names an entity. It interacts with articles, determiners, forms plurals, and controls verb agreement and pronoun choice.
Diagnostic: can you put the/a before it or pluralise it? → noun. Does it describe an action with tense? → verb. Can it do both? → check the sentence context.
Verb
Verb vs noun vs adjective: nouns name things. Adjectives describe. Verbs express what happens or what IS. The test: can it take tense (walked, will walk)? Can it take -ing? Can it follow to as an infinitive (to walk)? Yes to any → verb. English often converts freely between classes (run = noun or verb), so context decides.
A verb = action/state/occurrence word. 5 forms (base, -s, past, past participle, -ing). Carries tense, aspect, mood, voice. The one required element in every sentence.
Diagnostic: does it change for tense (walk → walked)? Can you put to before it (to walk)? Does it take -ing (walking)? → verb.
C1 | Advanced
C1 vs C2: C1 means fluent and flexible use with occasional gaps in very unfamiliar domains. C2 means native-like command of idiom, irony, and register across any subject. If you can handle advanced grammar but still miss cultural nuance or very rare idioms, you're C1.
C1 is the advanced CEFR level: inversion, cleft sentences, subjunctive mood, advanced conditionals, and precise register control in professional and academic contexts.
Diagnostic: can you write persuasively in different registers and catch subtle irony? Consistently → C2. Sometimes → 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.