A:acting out
B:bringing out
C:giving out
D:working out
Most people think ________ necessary to learn a foreign language nowadays.
CO(g)+ 12 O2(g)= CO2(g) ΔH=−283.0 kJ·mol−1②
C(石墨)+O2(g)= CO2(g) ΔH=−393.5 kJ·mol−1③
则4Fe(s)+3O2(g)= 2Fe2O3(s)的ΔH为( )