Premier Wen Jiabao said that if we worked hard and ________ optimistic, we were ________ win the

war against the swine flu.[ ]

A．were; bounding  

B．were; bound to

C．was; bounding to  

D．had; bounded to

C₈H₁₈经多步裂化，最后完全转化为C₄H₈、C₃H₆、C₂H₄、C₂H₆、CH₄五种气体混合物。该混合物的平均相对分子质量可能是 [ ]

A.28

B.29

C.39

D.40