这种用法常与以下时间状语连用：

★表示不确定的过去时间状语（already, before, lately, recently, yet等）。如：

　I haven't seen that movie yet.

★表示频度的时间状语（ever, never, always, often, rarely, sometimes, once, twice, three times等）。如：

　North Americans have always liked cars.

　He has been absent three times this term.

2. 表示动作或状态从过去某时开始，继续到现在，可能继续下去，也可能刚刚结束。如：

　He has visited China for three days.

　For years I have been interested in mathematics.

这种用法常与以下时间状语连用：

★由since引导的时间状语。要注意since用作介词，后跟表时间的短语时，必须是确定的时间点，而不能是一段时间。如：

　They have done colour painting in China since the 12th century.

　We have known each other since we were children.

★由for引导的时间状语。for后跟的是表示一段时间的短语，不能跟时间点。如：

　He has lived in Shanghai for two years.

【拓展】现在完成时、一般过去时和一般现在时三者的区别：

　　现在完成时强调过去发生的动作对现在的影响或者结果，它必须与现在的情况有联系。一般过去时只表示过去的事情，与现在的情况没有联系。一般现在时则强调经常发生的动作或存在的状态。如：

He has opened the window.

He opened the window this morning.

He often opens the window in the morning.

【即学即练】

I. 选用括号内合适的内容补全下面句子。

1. My sister ________ (has been / was) interested in medicine ever since she ________ (has been / was) a child.