Explanation:

- Option 1: Prevention of frauds

- Internal check is designed to prevent fraud by ensuring that no single employee has control over all aspects of a financial transaction.

- Option 2: Detection of frauds

- While internal checks can reveal fraud, their primary purpose is to prevent it before it occurs.

- Option 3: Helping audit is depth

- Internal checks assist auditors by ensuring that records are truthful, but the primary aim is not to facilitate audits.

- Option 4: Detection of errors

- Detecting errors can occur as a byproduct of internal checks, but prevention is the main goal.

Option 1: Prevention of frauds is the correct answer.