If you don't know that _____ is the mother of success, you are sure to be _____ in life.    [ ]

A. failure; failure  

B. a failure; a failure  

C. a failure; failure  

D. failure; a failure

甲、乙、丙、丁是初中化学中常见的四种物质，它们有如下反应关系： ①甲+丁→H₂O ②乙+丁→CO₂ ③丙+丁→H₂O+CO₂。则丙为 [ ]

A．H₂

B．CH₄

C．C₂H₅Cl

D．CO