a.C(s)+H2O(g)=CO(g)+H2(g) △H1=Q1kJ•mol-1①
H2+O2(g)=H2O(g) △H2=Q2kJ•mol-1②
CO(g)+O2(g)=CO2(g) △H3=Q3kJ•mol-1③
b.C(s)+O2(g)=CO2(g) △H4=Q4kJ•mol-1④
下列说法正确的是( )