Concept:Periodic maintenance means servicing a machine at fixed time or usage intervals, not just minor daily checks.
Explanation:Checking radiator water, checking tyre pressure, and cleaning after use are routine checks done frequently, often before or after each work session.
Changing engine oil, however, is carried out according to a set schedule based on hours of use or distance covered.
It ensures proper lubrication of the engine and reduces wear over time.
So, among the given options, the periodic maintenance activity is changing engine oil.
Answer:C. changing engine oil
