Something ________ otherwise he ________ here then. [ ]

A. must happen; would have been

B. must have happened; would be

C. must have happened; would have been

D. would happen; would be

已知瓦斯的主要成分是CH₄。将一定量的CH₄在O₂中点燃，CH₄已完全反应，燃烧产物为CO、CO₂和H₂O(g)，此混合气体的质量为49.6g，当其缓缓通过足量的干燥的CaCl₂时，固体增重25.2g。原燃烧产物中

CO₂的质量为 [ ]

A. 12.5g

B. 19.7g

C. 13.2g

D. 24.4g