do you water these flowers?- Once a week.A. How soonB. How oftenC. How longD. How m

问题补充：

--- do you water these flowers? --- Once a week.

A. How soon

B. How often

C. How long

D. How much

答案：

A. How soon

(答案→)B. How often

C. How long

D. How much

解析：根据答语内容- Once a week.，可知问句的特殊疑问词how often，故选B

故用B