短暂性动词是表示瞬时动作完成的意思，用于完成时不能和表示一段时间的状语用在一起，并不是不能用于完成时。
例子：
He has finished his homework.
He has finished his homework for three days.(结束不需要三天)
Now it has become a very beautiful city.
He has become a professional singer since 2005.(要改为been)
He was born in 2000,
He has been born for 8 years .(明显是不对了)