Question

---_______do you send e-mails to your pen friend?  ------Once a month.

A．How long

B．How far

C．How much

D．How often

Answer 1

D

解析试题分析：句意：你多久给你的笔友发一封电子邮件？一个月一次。How long多长；How far多远；How much多少（后跟不可数名词）；How often 多久。故选D。 
考点: 考查疑问词的用法。