Present Perfect Revision

The time expression “for” is used to talk about the quantity of time.

The sentence “Koreans have built many skyscrapers” expresses that they are in the processes of building many skyscrapers.

The sentence “Korean population has been growing since 1900 at a rate of 25%” expresses that the population continues to grow.

The form “Present perfect” (both simple and continuous) connects present to past.

The time expression “since” expresses the moment the action started and implies continuation until the present.

The sentence “I’ve known my best friend many years” expresses a finished action.

The auxiliary “have or has” depends on the previous word in the sentence.

After the auxiliary “have or has” the form of the action verb is always in the past.

In the question form, all the verbs change position.