现在完成时（Present Perfect Tense）描述在过去不确定时间发生的动作，强调的是一个动作的结果，因此动作什么时候发生不重要，这也就是为什么它通常不跟时间状语连用，让我们把现在完成时和不确定时间一起使用的情况分解一下。
在没有描述实际事情的情况下描述你曾经做过的事情，这种情况也常见于否定句中，例如：解析：我有去过法国的经历，但是这种经历没有跟具体的时间联系起来，只是之前的某个时间点去过。They have seen the movie.解析：他们有看过这部电影的经历，但是这种经历没有跟具体的时间联系起来，只是之前的某个时间点看过。He has never traveled by train.解析：他从来没有乘火车旅行过的经历，没有具体的时间与之联系起来。I’ve never been to a professional baseball game.解析：我从来没看过职业棒球赛的经历，没有具体的时间与之联系起来。
The company has evolved over time.The government has become more interested in arts education.My English has really improved since I moved to Australia.They have grown fond of their new step father.
The lab has discovered many treatments for cancer.Our son has learned how to read.Doctors have cured many deadly diseases.Scientists have developed a new way to fight the virus.
Susan hasn't mastered Japanese, but she can communicate.Bill has still not arrived.It hasn’t stopped raining.He hasn’t finished milking the cows.
The company has spoken with several technicians, but they can’t find someone who can erase the virus.公司已经和几位技术人员谈过了，但他们找不到能清除病毒的人。We’ve had many problems while building our house.I have had four quizzes and five tests so far this semester.到目前为止，我这学期已经有四次小测验和五次测验了。We have had many major problems while working on this project.
在谈论某个时间范围内而不是在某个时间发生的事情时，仍然可以使用现在完成时，如 in the past month，in the past year，this month，up to this point，so far 和 recently 等等，例如：My car has broken down three times in the past month.We’ve visited my mother in the hospital six times in the past two weeks.The company has hired four managers in the past two years.They have had three tests in the last week.
She graduated from university less than three years ago. She has worked for three different companies so far.
她大学毕业不到三年。到目前为止，她在三家不同的公司工作。
He's had a really rough time recently.注意：last year 和 in the last year 在意思上大相径庭，last year 指的是现在之前的一年，是一个时间点，因此要与一般过去时连用，而 in the last year 指的是现在之前的365天，不是一个时间点，因此要与现在完成时连用，其他类似的也一样，例如：I have been to Mexico in the last year.
