To keep the budget on track throughout the project, the project manager should use metrics like Cost Performance Index (CPI), Earned Value Management (EVM), and variance analysis. These tools provide early indicators of cost deviation and allow timely corrective actions.

According to the PMBOK® Guide – Seventh Edition, measuring performance using reliable cost metrics is essential in the Monitoring and Controlling phase of Cost Management.

Option A is reactive and does not prevent overruns.

Option B (baselining) is necessary but not sufficient for tracking throughout the project.

Option C is selective and does not address holistic cost control.