Explanation:

- Fiscal Measures: These involve changes in government spending and taxes. By increasing government expenditure or reducing taxes, aggregate demand can be boosted to correct deficient demand.

- Monetary Measures: These include altering interest rates or changing the money supply. Lowering interest rates or increasing the money supply can stimulate spending and investment, thus correcting deficient demand.

- Option 3 - Both (a) & (b): Using a combination of fiscal and monetary policies can effectively address deficient demand by boosting overall economic activity.

- Option 4 - None of the above: This is incorrect since fiscal and monetary measures are standard tools for managing demand levels.

Correct Answer: Option 3 - Both (a) & (b)