下列反应符合生成热的定义是（B）
A S(g) + O2(g) = SO2(g);
B S(s) + 3/2O2(g) = SO3(g)
C S(g) + 3/2O2(g) = SO2(g);
D S(s) + 3/2O2(g) = SO2(s).