2014 2015 Real GDP growth (annual percent) 4.6 4.9 Inflation (annual percent) 6.2 6.6 Interest rate (nominal, annual percent) 7.3 7.9 Government deficit (primary, percent of GDP) 4.9 2.7 Government deficit (total, percent of GDP) 6.1 6.2 Government debt (end of period, percent of GDP) 40.0 ? The debt-to-GDP ratio equation: 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". What is the contribution of the economic growth of 2015 to the debt-to-GDP ratio of 2015? A. -3.1% B. 2.6% C. -1.8% D. 0.5%