In the following English grammar question on voice, choose the correct passive form of the sentence: He had transported all his equipment to his factory.

Introduction / Context:
This question tests your skill in converting a past perfect active sentence into its correct passive counterpart. The original sentence is He had transported all his equipment to his factory. The focus here is on an action completed before some other point in the past. In passive voice, we want to highlight the equipment and the result of the action rather than the person who did it, while preserving the past perfect time reference.

Given Data / Assumptions:

• Active sentence: He had transported all his equipment to his factory.
• Subject: He
• Verb phrase: had transported (past perfect, active)
• Object: all his equipment
• Place complement: to his factory
• Task: Select the passive sentence that keeps the same tense and meaning.

Concept / Approach:
For past perfect tense, the passive structure is had been + past participle. The object all his equipment becomes the grammatical subject of the passive sentence, and the original subject he is optionally included in a by phrase. Therefore, had transported must become had been transported in passive voice. The phrase to his factory remains unchanged as a place complement at the end of the sentence. The resulting passive sentence is All his equipment had been transported by him to his factory.

Step-by-Step Solution:

Verification / Alternative check:
To verify, reverse the process. Start from All his equipment had been transported by him to his factory and convert to active: He had transported all his equipment to his factory. This matches the original sentence exactly in tense, subject, object, and place complement. The time relationship (completed before another past event) encoded by the past perfect is preserved through the had been structure.

Why Other Options Are Wrong:
Option A (All his equipment are transported to his factory by him.) changes the tense to simple present passive are transported, which does not match the original past perfect sense. Option B (All his equipment were transported to his factory by him.) uses simple past passive were transported, again losing the perfect aspect. Option C (All his equipment have transported by him to his factory.) is ungrammatical because have transported is missing a passive auxiliary and incorrectly agrees with equipment. Option E (All his equipment is being transported by him to his factory.) uses present continuous passive, suggesting an action happening now, which clearly differs from a completed past action.

Common Pitfalls:
Students often simplify past perfect to simple past when changing voice, but this changes the meaning about when the action occurred. Another common error is forgetting to include been in the passive perfect structure (had been transported) and writing forms like had transported by him, which are incorrect. It is also easy to confuse subject–verb agreement with collective nouns like equipment, which is grammatically singular but logically plural; however in this sentence, had been is used with equipment as a singular mass noun, and that is acceptable. Always keep the auxiliary sequence correct: had been + past participle for past perfect passive.

Final Answer:
The correct passive-voice transformation is All his equipment had been transported by him to his factory.