Final answer:
Therefore, the correct option is d. Debt-to-GDP ratio in the U.S. increased following the tax reforms in the 1980s.
Step-by-step explanation:
The false statement is option d. Debt-to-GDP ratio in the U.S. increased following the tax reforms in the 1980s.
According to the provided information, the debt/GDP ratio in the U.S. increased since the early 1980s (option c), but it does not specifically state that it increased following the tax reforms in the 1980s (option d).
Therefore, the correct answer is option d. Debt-to-GDP ratio in the U.S. increased following the tax reforms in the 1980s is false.