In which of the following cases does the size of the government’s debt and the size of the budget deficit indicate potential problems for the economy?

a. The government’s debt is relatively low, but the government is running a large budget deficit as it builds a high-speed rail system to connect the major cities of the nation.

b. The government’ debt is relatively high due to a recently ended deficit- financed war, but the government is now running only a small budget deficit.

c. The government's debt is relatively low, but the government is running a budget deficit to finance the interest payments on the debt.

d. The government's debt is relatively high and the government is running a budget deficit to finance new infrastructure spending.