The correct answers are I must have stepped on a butterfly and altered the course of history and I will travel to 1920, and my assistant, to 1930.
I must have stepped... and altered...
This is a correct example of subject and auxiliary ellipsis. The subject "I" and the auxiliaries "must have" are successfully shared between the two coordinated verbs ("stepped" and "altered").
I will travel to 1920, and my assistant, to 1930.
This is a flawless example of gapping. The verb phrase "will travel" is perfectly understood and omitted in the second clause.
Incorrect options:
"...and my assistant has, the temporal maps" is ungrammatical. You cannot leave the auxiliary "has" stranded right before a new direct object when gapping the main verb.
"...and my assistant did too" is ungrammatical. The first clause is in the passive voice ("was chased"), but "did" attempts to substitute for an active verb phrase. They do not match.
Coordination
- ✅ I like reading, swimming, and cooking. — parallel verb forms
- ❌ I like reading, swim, and to cook. — broken parallelism
- ✅ She is smart and hardworking. — adjective + adjective
- ❌ She is smart and works hard. — adjective + clause (mismatched)
Coordination links grammatically equal elements with a coordinating conjunction (and, or, but). The golden rule: all items in a coordinated structure must be the same form.
Test: replace the conjunction with a bullet list. Do all items have the same grammatical shape? If not, you have a parallelism error.
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.
Modal verb
- ✅ She can swim. — ❌ She can to swim. (modal + bare infinitive, no to)
- ✅ You must leave now. — strong obligation
- ✅ It might rain. — possibility (~50%)
- ✅ He should apologise. — advice/recommendation
Modal verbs (can, could, may, might, must, shall, should, will, would) are auxiliaries expressing ability, permission, possibility, obligation, or speculation. Always + bare infinitive. Never inflected (she can, not she cans).
Rule: modals never take to after them, never add -s for third person, and can't combine directly (must can ❌ — use must be able to).
Passive voice
- ✅ The meal was cooked by the chef. — passive (action matters)
- ✅ Mistakes were made. — passive, agent hidden (evasive)
- ✅ Active: The chef cooked the meal. — stronger, clearer
- ❌ The report was being been written. — malformed passive
The passive = be + past participle. Object becomes subject. Use it when the doer is unknown, irrelevant, or obvious. Avoid when it hides responsibility or weakens prose.
Formula: find the active object → make it the subject → use be (matching tense) + past participle → optionally add by + agent.
Sentence
- She left. — simple (one independent clause)
- She left, and he stayed. — compound (two independents)
- She left because she was tired. — complex (independent + dependent)
- She left because she was tired, and he stayed. — compound-complex
A sentence = one or more clauses forming a complete thought, ending with terminal punctuation. Four types based on clause structure: simple, compound, complex, compound-complex.
Minimum requirement: at least one independent clause with a subject + finite verb. Without that → fragment.
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.