O2(g)=== CO(g) △H1 = -110.5 kJ• mol-1 C(s)+O2(g) === CO2(g) △H2= -393.5 kJ• mol-1 则C(s)+CO2(g)=== 2CO(g) 的△H 为
A:+283.5 kJ• mol-1
B:+172.5 kJ• mol-1
C:-172.5 kJ• mol-1
D:-504 kJ• mol-1