In this English fill-in-the-blank question on passive voice and subject–verb agreement, choose the correct option to complete the sentence: "The gate _______ by the watchman on duty." Select the grammatically correct and most natural alternative.

Introduction / Context:
This question tests your understanding of passive voice construction and subject verb agreement in English. The sentence describes an action performed by the watchman on the gate. The presence of the agent phrase "by the watchman on duty" strongly suggests a passive construction, and the verb phrase must match the singular subject "gate" in tense and number.

Given Data / Assumptions:

• Sentence fragment: "The gate _______ by the watchman on duty."
• Options:
  • "opened"
  • "was opened"
  • "were opened"
  • "was opening"
  • "had opened"
• The subject "The gate" is singular.
• The phrase "by the watchman on duty" indicates who performed the action, which is typical in passive sentences.
• We assume a simple past event: the watchman opened the gate.

Concept / Approach:
In passive voice, we use a form of the verb "be" plus the past participle of the main verb: "was opened", "is opened", "has been opened", etc. The auxiliary verb "be" must agree with the subject in number and tense. Here, "gate" is singular, and a simple past action is implied, so "was opened" is the most appropriate choice. Other options either fail to mark the passive properly or show incorrect agreement or aspect for this context.

Step-by-Step Solution:
Step 1: Recognise from the phrase "by the watchman on duty" that the sentence is in the passive voice. Step 2: Identify the subject "The gate". It is singular, so any auxiliary verb must also be singular. Step 3: The correct passive structure in the simple past tense is "was opened": "The gate was opened by the watchman on duty." Step 4: Check each option: - "opened" alone suggests an active construction like "The watchman opened the gate", which does not fit the given frame. - "was opened" is passive simple past and agrees with a singular subject. - "were opened" is plural and wrong for the singular "gate". - "was opening" is past continuous and would normally require a different structure (e.g., "The gate was opening slowly"), not "by the watchman". - "had opened" is past perfect but would typically be used in an active form "The watchman had opened the gate". Step 5: Thus, "was opened" is the only option that fits both the grammar and the context.

Verification / Alternative check:
Reconstruct the full sentence with the correct option: "The gate was opened by the watchman on duty." This is a standard passive sentence and sounds natural. If you replace "was opened" with "were opened", the sentence becomes ungrammatical because "were" disagrees with the singular subject. Replacing it with "opened" alone leaves the auxiliary missing. This comparison confirms "was opened" as the correct choice.

Why Other Options Are Wrong:

• opened: Missing auxiliary; cannot stand as a passive verb phrase in this frame.
• were opened: Verb is plural and does not agree with the singular subject "gate".
• was opening: Past continuous; combined with "by the watchman" it is awkward and does not match the simple event description implied by the context.
• had opened: Past perfect in active voice; would require a different sentence structure (e.g., "The watchman had opened the gate.").

Common Pitfalls:
A frequent mistake is to forget the auxiliary verb "be" in passive constructions or to choose the wrong form ("were" instead of "was"). Another pitfall is confusing continuous and simple aspects; "was opening" suggests an ongoing process, not a completed action. In exam questions, recognise phrases like "by the..." as strong clues that a passive structure is required and then apply the correct form of "be" plus the past participle.

Final Answer:
The correct completion is "was opened", giving the sentence: "The gate was opened by the watchman on duty.".