— ____________ do you help your mother do the housework?

— Once a week. [ ]

A. How often

B. How long

C. How much

对下列有机反应类型的认识中，正确的是[ ]

A．；取代反应

B．CH₂＝CH₂ ＋ Br₂→CH₂Br－CH₂Br；加成反应  

C．2CH₃CH₂OH+O₂2CH₃CHO+2H₂O；取代反应

D．CH₃COOH + CH₃CH₂OHCH₃COOCH₂CH₃+H₂O；酯化反应