twice，主要用作为副词，例如：

1、We go there maybe once or twice a month.我们每月大概去那里一到两次。

2、You should visit your dentist at least twice a year.你应该每年至少去看两次牙科医生。

3、New drivers have twice as many accidents as experienced drivers.新驾驶员所出的事故是老驾驶员的两倍。