Answer: Option (C) is correct.
Explanation:
Correct option: A $50 billion decrease in government spending would be the most contractionary fiscal policy.
A. Increase the taxes by $40 billion is also a contractionary fiscal policy but it doesn't have a greater impact than decreasing the government spending by $50 billion.
B. It is an expansionary fiscal policy.
D. There are both expansionary fiscal policy by decreasing taxes by $10 billion and contractionary fiscal policy by decreasing government spending by $40 billion. But it doesn't have much impact as the option (C) is having.
Therefore, Option (C) is having the most contractionary fiscal policy.