1 一段时间常用于完成时态, 尤其以现在完成时多为常见.
2 现在完成时态往往表示过去的动作对现在所造成的影响，因此常与段时间连用, 常用的段时间短语有over the years, over the past few years, in the past few years during the 10 years.还有for短语。例如 Great changes have taken place in my hometown in the past five years.
通常情况下，英语中一段时间用于现在完成时，表示动作或者状态的延续.譬如：We have studied English for about 5 years.
