Choose the correct passive form of the given sentence:
The watchman locks the school gate when the last bus leaves.
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → The school gate is locked by the watchman when the last bus leaves.
Passive of a sentence with two clauses:
| Change | Active | Passive | Why |
|---|---|---|---|
| Object becomes subject | the school gate | The school gate | The gate receives the action, so it becomes the subject. |
| Tense kept | locks | is locked | “Locks” is in the simple present, so the passive stays in the simple present: is / are + past participle (V3). “Is” because the gate is one. |
| Agent (by ...) | The watchman | by the watchman | The watchman is named, so the doer comes after “by”. |
| Second clause kept | when the last bus leaves | when the last bus leaves | “Leaves” has no object here. So it cannot become passive and stays as it is. |
| Full sentence | The watchman locks the school gate when the last bus leaves. | The school gate is locked by the watchman when the last bus leaves. |
In other sentences with two clauses, change only the verb that has an object. Example: The cook switches off the gas when the dal boils. → The gas is switched off by the cook when the dal boils.
Why the Other Options are Incorrect?
Option 1: The school gate is locked by the watchman when the last bus is left. — Incorrect. “Is left” wrongly makes “leaves” passive. “Leaves” has no object, so it must stay “leaves”.
Option 2: The school gate was locked by the watchman when the last bus leaves. — Incorrect. “Was locked” is the simple past. The active “locks” is the simple present.
Option 4: The school gate is being locked by the watchman when the last bus leaves. — Incorrect. “Is being locked” is the present continuous. The active is “locks”, not “is locking”.