2014 2015 Real GDP growth (annual percent) 3.6 3.9 Inflation (annual percent) 5.2 5.6 Interest rate (nominal, annual percent) 6.3 6.9 Government deficit (primary, percent of GDP) 3.9 1.7 Government deficit (total, percent of GDP) 5.1 5.2 Government debt (end of period, percent of GDP) 35.0 ? Bt/Yt Bt-1/Yt-1 (it-t)Bt-1/Yt-1 - gtBt-1/Yt-1 Dt/Yt . Bt - government debt, Yt - nominal GDP, it - nominal interest rate, t - inflation rate, gt - compounded GDP growth rate, Dt - primary deficit, t - year. Each term is referred to as "contribution of". When the contribution of the economic growth to the debt-to-GDP ratio is positive? A. Real GDP growth is zero. B. Real GDP growth is positive. C. Never. D. Real GDP growth is negative