Answer:
The correct answer is A. increased by $20 billion.
Explanation:
If you take the sum of the decreed values in deficit for years 1 and 2, you would have that the total amount of credits is $ 90 billion. On the other hand, for years 3 and 4 there are positive values for a total of $ 70 billion.
By the end of year 4 you have to have a pending balance of $ 20 billion, which is the result of subtracting the deficit minus the net surpluses generated in years 3 and 4.