In the following question, a sentence is divided into four parts. Identify the part that contains an error in standard English usage, or select 4 if there is no error: This is one of London’s most (1)/ important and ancient axial routes, (2)/ roughly following the line of (3)/ a Roman through-road. (4)

Introduction / Context:
This error-spotting question presents a descriptive sentence about one of London's ancient axial routes. Your task is to check each part for grammatical errors or awkward usage. If all parts are correct, you should select 4 to indicate No error. Such questions test your ability to recognise well-formed complex sentences in English.

Given Data / Assumptions:
- (1) This is one of London’s most
- (2) important and ancient axial routes,
- (3) roughly following the line of
- (4) a Roman through-road.
- The sentence describes a particular route in London that follows an old Roman road.
- We must focus on grammar and standard expression, not on historical details.

Concept / Approach:
The main concepts here are the correct use of one of + superlative structure, correct adjective order, and proper use of present participle phrases. The phrase one of London’s most important and ancient axial routes is correctly formed, with most modifying both important and ancient. The participial phrase roughly following the line of a Roman through-road properly modifies routes. There is no disagreement between subject and verb, and the sentence flows naturally as one unit.

Step-by-Step Solution:
Step 1: Examine part (1): This is one of London’s most. This introduces a standard structure: This is one of + superlative + plural noun.Step 2: Part (2): important and ancient axial routes, completes that structure: most important and ancient axial routes. This is grammatically acceptable and stylistically sound.Step 3: Part (3): roughly following the line of is a present participle phrase which describes how the route is oriented. It is correctly attached to the noun phrase axial routes and is fine.Step 4: Part (4): a Roman through-road, provides the object of the preposition of and clearly refers to a type of Roman road. The hyphenated term through-road is acceptable in descriptive writing.Step 5: None of the parts contains a grammatical error or an awkward construction that examiners typically test.Step 6: Therefore, the sentence is correct as it stands, and the appropriate choice is 4, indicating No error.

Verification / Alternative check:
Combine all parts into one sentence: This is one of London’s most important and ancient axial routes, roughly following the line of a Roman through-road. This sentence reads smoothly, uses correct article and preposition choices, and follows normal patterns of English description. There is no need to change word order, verb forms, or prepositions. Since every section passes grammatical checks, the only valid answer is No error.

Why Other Options Are Wrong:
- Option 1 cannot be marked wrong because This is one of London’s most is a standard opening structure.
- Option 2 shows correct superlative usage and adjective order.
- Option 3 correctly uses a participial phrase (roughly following the line of) to modify routes.
- Option 4 contains a well-formed noun phrase a Roman through-road and does not introduce any error.

Common Pitfalls:
Some learners may feel unsure about compound adjectives like axial routes or through-road and assume they must be wrong. Others may mistakenly think that most important and ancient should be rewritten, but English allows most to modify a pair of adjectives. Another common pitfall is over-editing correct sentences because they sound complex. When answering error-spotting questions, always ask whether you can clearly state a standard grammar rule that is being broken; if not, consider that the sentence may be correct.

Final Answer:
The sentence has no grammatical error, so the correct choice is option 4 (No error).