English grammar – Spot the error (choose the part with an error or “No error”). Inversion pattern: Scarcely had / he gone / when a policeman / knocked at the door.

Introduction / Context:
This sentence uses the standard correlative “Scarcely … when …” with inversion and perfect aspect to mark near-simultaneous past events. The task is to see whether any segment is ungrammatical.

Given Data / Assumptions:

• Auxiliary “had” plus past participle “gone.”
• Conjunction “when” introducing the second event.
• Simple past “knocked” for the following action.

Concept / Approach:
All parts are correct: “Scarcely had he gone when …” is a recognized formal pattern (alternatively, “Hardly had … when …”). The sequence “past perfect” for the earlier event and “simple past” for the subsequent event is appropriate.

Step-by-Step Check:

Verification / Alternative check:

Why Other Options Are Wrong:

Common Pitfalls:

Final Answer:
No error.