Answer:
The answer is B. increase its spending.
Explanation:
Fiscal policy is a tool used by the government of every nation to control its economy. It uses its spending and revenue (tax) to control it.
When the economy is operating at an output level below potential real GDP, it means there are low activities in the economy i.e reduced households' consumption, reduced business investments and reduced government spending.
Government can stimulate the economy (which will increase real GDP) by increasing its spending in all areas.
Increasing taxes will reduce GDP because households' consumption will reduce due to lower disposable income and business investments too will reduce.
Option A and D are wrong because money supply is a monetary policy.