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。
