Choose the correct passive voice transformation of the sentence: "The teachers informed the students that the class had been cancelled."

Introduction / Context:
Mastering active and passive voice transformation is essential for both grammar tests and formal writing. This question involves a slightly longer sentence that includes a reporting clause and a reported clause about a cancelled class. You are asked to choose the passive version that best preserves both the tense and the meaning of the original active sentence: The teachers informed the students that the class had been cancelled.

Given Data / Assumptions:

• The original subject is the teachers.
• The original direct object is the students.
• The reported information is that the class had been cancelled, already in passive past perfect.
• We must change the main clause to passive while keeping the reported clause intact.

Concept / Approach:
To form the passive, the direct object of the active sentence becomes the subject of the passive sentence. The main verb informed must change into an appropriate passive form, and the tense should remain simple past. The reported clause that the class had been cancelled already has its own correct passive form and does not normally change. Therefore, we expect a structure like The students were informed by the teachers that the class had been cancelled. This keeps the past perfect in the reported clause and uses were informed as the simple past passive equivalent of informed.

Step-by-Step Solution:
Step 1: Identify the main clause: The teachers informed the students, where teachers is the subject and students is the object. Step 2: Convert the main clause into passive by making the students the new subject and using were informed as the simple past passive. Step 3: Keep the agent the teachers in a by phrase: by the teachers. Step 4: Attach the reported clause that the class had been cancelled unchanged, because it already correctly indicates that the cancellation happened before the informing. Step 5: Compare the result The students were informed by the teachers that the class had been cancelled with the options and select the matching sentence.

Verification / Alternative check:
Check that the timeline still makes sense. The class had been cancelled is in past perfect, indicating that the cancellation occurred before the time when the teachers informed the students. The passive version The students were informed by the teachers that the class had been cancelled maintains this order: first cancellation, then informing. Also verify that the main verb informed remains in simple past as were informed, keeping the time reference the same as in the original sentence. This confirms that Option C is the most accurate transformation.

Why Other Options Are Wrong:
Informing the students that the class is cancelled was done by the teachers.: This is wrong because it changes the tense in the reported clause to is cancelled, which implies present time, and it uses an awkward gerund structure rather than a clear passive sentence.
The class has been cancelled, this the teachers informed the students.: This is wrong because it is poorly structured and does not present a correct passive form of the main clause. It reads like two fragments joined incorrectly.
The teachers cancelled the class and informed the students.: This is wrong because it remains in active voice and adds an extra idea that the teachers themselves cancelled the class, which was not clearly stated in the original.

Common Pitfalls:
A frequent mistake is to alter the tense in the reported clause while changing the main clause to passive, which can disturb the original time relationship between events. Another pitfall is thinking that any sentence with by the teachers must be correct passive, even if the overall structure is awkward or ungrammatical. To avoid errors, always convert the main clause step by step and leave correctly formed subordinate clauses as they are unless there is a specific reason to change them.

Final Answer:
The correct passive transformation is The students were informed by the teachers that the class had been cancelled.