twice的词性和用法

例句：

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。

4、You should think twice about employing someone you've never met.

雇用素不相识的人应三思而行。