It was until last year that he ______.

A．left his home town for a new start 　

B．came to realize the importance of leaving English

C．worked as an English teacher at a middle school 　

D．set out to build a new house of h his own

已知液化石油气气相的各组分质量成分为：gC₃H₈=50%，gC₄H₁₀=50%，在标准状态下的平均动力黏度为（）。[各组分的动力黏度（10^-6Pa·s）为：C₃H₈=7.65，C₄H₁₀=6.97]

A．2.147×10^-6Pa·s

B．5.168×10^-6Pa·s

C．7.294×10^-6Pa·s

D．8.434×10^-6Pa·s