- _______ do you go back to your hometown to visit your grandparents?

- Twice a year: Usually at Mid-Autumn festival and during the Chinese New Year.

A．How long

B．How often

C．How much

D．How many

制定热网站外网系统的清洗方案要考虑（）。

A、水源

B、水质

C、清洗效果

D、清洗方法。