A

Explanation:

Senior management has the primary responsibility for detecting fraud in a company because they are responsible for establishing and maintaining effective internal controls and governance processes to prevent and detect fraudulent activities. While external auditors (B) assess the risk of material misstatement due to fraud, their role is not primarily to detect fraud but to provide assurance on financial statements. Police authorities (C) investigate fraud after it is reported, not as a preventive measure within the company. Internal auditors (D) contribute to fraud detection through their evaluation of internal controls, but the ultimate responsibility lies with senior management, as they oversee the company’s operations and control environment.