present perfect

基本解释

When you ask about something that started in the past but continues to the present time, you use the Present Perfect tense, e.g.
儅你談論從過去開始一直持續到現在的某件事時，用現在完成法時態。
edu.sina.com.cn
When you ask about something that started in the past but continues to the present time, you use the Present Perfect tense, e.g.: I’ve been there for 5 years / I’ve been there for 5 years.
儅你談論在過去開始但是一直持續到現在的某事時，用現在完成時態，例如：I’ve been there for 5 years/我在那裡已經5年了。
edu.sina.com.cn
If we say when a past event happened (for example, by using time-adverbs), we do not usually use the present perfect.
說過去發生的事件（例如：用過去時間狀語），我們通常不用現在完成時。
blog.sina.com.cn

This pullback could present the perfect buying opportunity.
FORBES: Buy BBBY While Shares Are Below Recent Highs
But just like the guy who bought the older Volkswagen off my dad, I rarely believe those who present everything as perfect without any dents or challenges.
FORBES: How To Sell Without Being A Salesperson
Pick-n-mix, and you have the perfect millennium present.
ECONOMIST: Shakespeare on tape: Audio-Bard

In grammar, the present perfect tenses of a verb are the ones used to talk about things that happened before the time you are speaking or writing but are relevant to the present situation, or things that began in the past and are still happening. The simple present perfect tense uses "have" or "has" and the past participle of the verb, as in "They have decided what to do."