The correct answers are She and the butler were seen near the vault. and They were seen near the vault.
When a pronoun is performing the action (acting as the subject of the sentence), you must use subject pronouns like she or they. Object pronouns like her or them cannot be the subject of a sentence, even when paired with another noun like "the butler".
Pronoun
Pronoun vs noun: nouns name explicitly (Sarah, the book). Pronouns substitute and point back (she, it). Pronouns are a closed class (you can't invent new ones easily), while nouns are open (new ones appear constantly). The main complication: pronouns still carry case marking that nouns have lost.
A pronoun replaces a noun or noun phrase. Types: personal, demonstrative, relative, interrogative, reflexive, indefinite.
Diagnostic: every pronoun must have a clear antecedent (the noun it replaces). If the reader can't tell which noun a pronoun refers to → ambiguity error.
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.
English Grammar Basics
Basics vs intermediate/advanced grammar: if you're unsure whether to study articles or conditionals, tense basics or reported speech — you need to check whether your foundations are solid first. Basics covers everything up to A2.
English Grammar Basics groups the core building blocks: nouns, verbs, adjectives, prepositions, present/past tenses, questions, and negation.
Diagnostic: if you still hesitate over she don't vs she doesn't, or a vs an — start here. Master these and intermediate topics stop feeling random.
A2 | Elementary | Pre-intermediate
A2 vs B1: A2 handles routine transactions and simple past narration. B1 handles connected discourse, explaining reasons, and understanding main points in clear standard speech. If you can tell what happened but not why it matters, you're still A2.
A2 is the elementary level of the CEFR: past simple, present perfect, first conditional, basic modals, and routine communication about familiar topics.
Diagnostic: can you link ideas with because, although, so that and hold a conversation beyond scripted topics? No → A2. Yes → moving into B1.
Easy
Easy vs Medium vs Hard: Easy = one rule, obvious answer, A1–A2. Medium = one rule but realistic distractors, A2–B1. Hard = interacting rules, edge cases, B2+. Start Easy to check you have the basics before moving up.
The Easy tag filters for single-rule, short-sentence, common-vocabulary challenges designed for beginners or for anyone wanting a confidence check on fundamentals.
Diagnostic: if you get Easy questions wrong, stay here — your foundations need work. If they feel trivial, move to Medium.