In a marine boiler water level control system, Proportional plus Integral (P+I) control is widely used instead of simple Proportional (P) control. What is the primary operational reason for adding the Integral action? (16)

(a) To eliminate steady-state offset caused by changes in steam demand.

(b) To instantly increase the response speed to sudden load changes.

(c) To decrease the maximum overshoot of the water level.

(d) To prevent the control valve from experiencing mechanical wear.

Briefly justify your answer.