Select the grammatically correct option to complete the rival's statement.
"He claims to understand the complex rules of 4D quantum chess, but I highly doubt he actually _____."
The correct answer is does.
This question tests the restriction on the substitution phrase do so. We use "do so" (or "do it") to replace an action (dynamic verb). However, we cannot use "do so" or "do it" to substitute for a state (stative verbs like understand, know, like, or own).
Instead, we must use standard ellipsis, leaving only the auxiliary verb does to stand in for "understands the complex rules."
Verb
- walk → walk / walks / walked / walked / walking (5 forms, regular)
- go → go / goes / went / gone / going (5 forms, irregular)
- be → am/is/are/was/were/be/being/been (8 forms)
- can → can / could (modal: only 2 forms, no -s, no -ing)
A verb is the one word class every English sentence requires. Carries tense (when), aspect (duration), mood (attitude), and voice (active/passive). Regular verbs add -ed; ~200 irregular verbs have unpredictable past forms.
Key insight: fix your verbs and most grammar problems disappear. Wrong tense, wrong agreement, wrong form — verb errors account for the majority of grammatical mistakes.
Auxiliary verb
- ✅ Do you know? — ❌ Know you? (English requires do-support for questions)
- ✅ She has finished. — ❌ She finished has. (auxiliary before main verb)
- ✅ They are leaving. — ❌ They leaving. (progressive needs be)
- ✅ He doesn't smoke. — ❌ He smokes not. (negation needs do)
Auxiliary verbs (be, have, do, and the modals) combine with main verbs to build questions, negatives, tenses, aspects, and passive voice.
Pattern: if you need to ask a question, negate, or stack tense/aspect — you need an auxiliary. The main verb carries meaning; the auxiliary carries grammar.
Present tense
- I work here. — simple present (habit/permanent)
- I am working now. — present progressive (happening right now)
- I have lived here for 10 years. — present perfect (started past, still true)
- I have been waiting for an hour. — present perfect progressive (duration up to now)
Four present tense forms: simple (habits/facts), progressive (now/temporary), perfect (past → present relevance), perfect progressive (ongoing duration). Each encodes a different relationship between the action and the present moment.
Trap: "I am living here for 10 years" ❌ — started in the past + still true = present PERFECT (have lived/have been living), not progressive.
Simple tense
- ✅ I go to work every day. — present simple (habit)
- ✅ She went home yesterday. — past simple (completed action)
- ✅ I will call you later. — future simple (promise/decision)
- ✅ Water boils at 100°C. — present simple (general truth)
The simple aspect is the default, unmarked verb form. Present simple = habits, facts, schedules. Past simple = completed actions. Future simple = predictions, promises, decisions. No auxiliary needed (except will for future and do for questions/negatives).
Rule: if the action is a fact, habit, completed event, or scheduled future — and you don't need to emphasise it being in-progress or connected to now → simple tense.
C1 | Advanced
- ✅ Not only did she finish early, but she also helped others. — inversion for emphasis
- ✅ It is the process that matters, not the result. — cleft sentence
- ✅ I insist that he be present. — formal subjunctive
- ✅ Were I to disagree, I would say so. — inverted conditional
These are C1 structures — the CEFR advanced level. At C1 you control inversion, cleft sentences, subjunctive forms, and register-switching fluently across formal and informal contexts.
Marker: if you can restructure a sentence for rhetorical effect without hesitation, you're C1.
Hard
- Had she not intervened, the situation would have escalated. — inverted conditional
- All distractors are grammatically plausible in other contexts
- Multiple rules interact (e.g., tense + aspect + modality)
- Context determines the answer — no single "rule" is enough
Hard marks upper-intermediate to advanced challenges: B2+, interacting rules, edge cases, plausible distractors, and contexts where pattern-matching fails.
Use "Hard" when Easy/Medium feel trivial and you want to test whether you actually understand a rule versus just recognising surface patterns.