A sentence is given in the active voice. Choose the option that best expresses the same idea in the passive voice: "The police arrested him on suspicion."

Introduction / Context:
This item tests your ability to convert a simple past active sentence into passive voice correctly and naturally. The active sentence is: The police arrested him on suspicion. In many reports, especially in newspapers, the focus is placed on the person who was arrested rather than on the police, so the passive form is frequently used. Your task is to choose the option that accurately represents this passive form without changing the tense or meaning.

Given Data / Assumptions:

• Active subject: The police.
• Verb: arrested (simple past).
• Object: him.
• Adverbial phrase: on suspicion.
• We need a passive sentence with he as the subject.

Concept / Approach:
To form the passive from a simple past active sentence, we use the pattern: object + was or were + past participle + by + subject. Here, the object him becomes the subject he in the passive. Because he is singular, we use was. The past participle of arrest is arrested. The phrase on suspicion remains as an adverbial, and by the police can be added to indicate the agent. Therefore, the correct passive sentence is: He was arrested on suspicion by the police.

Step-by-Step Solution:
Step 1: Turn the object him into the subject he in the passive sentence. Step 2: Use the simple past form of be, which is was, for the singular subject he. Step 3: Add the past participle arrested after was. Step 4: Keep the phrase on suspicion in place to describe the reason for the arrest. Step 5: Add by the police to identify the agent, giving the full passive: He was arrested on suspicion by the police.

Verification / Alternative check:
Compare the active and passive sentences for meaning and tense. The police arrested him on suspicion states that the police took action against him in the past because they suspected something. The passive He was arrested on suspicion by the police expresses the same finished action in the past, with he as the grammatical subject. The time reference and reason remain the same. None of the other options preserve this straightforward relationship without introducing tense errors or clumsy structures, so Option C must be correct.

Why Other Options Are Wrong:
Arresting him on suspicion has been done by the police.: This is an unnatural and wordy construction using a gerund phrase arresting him on suspicion instead of a clean passive verb form.
On suspicion the police had been arresting him.: This changes the tense to past perfect continuous had been arresting, suggesting repeated or ongoing action in the past, which does not match the original simple past action.
He has had been arrested on suspicion by the police.: This is grammatically incorrect because has had been arrested mixes auxiliary verbs incorrectly; the correct complex past passive would be he had been arrested, not has had been arrested.

Common Pitfalls:
Some learners overcomplicate passive forms by using unnecessary auxiliary verbs or nominalising the verb into phrases like arresting of. Others change the tense unintentionally, especially when they see had or has in options. To avoid these pitfalls, always focus on preserving the original tense and choosing the simplest possible be + past participle structure that fits the subject. Here, simple past was arrested is the best and most natural choice.

Final Answer:
The correct passive transformation is He was arrested on suspicion by the police.