The marks of the present perfect tense are: ready, however, just, never, once, before, since.

Already, already; Previously;

Used in affirmative sentences (after be verbs, auxiliary verbs and modal verbs, but before substantive verbs), it is often converted with yet. For example:

I have finished my work. ?

I have finished my work.

I haven't finished my work yet.

I haven't finished my work yet.

Replace it with a general question: Have you finished your work?

Second, still; But; Already; Do it again.

Put it at the end of negative sentences and general questions. Example:

I haven't heard from him yet. ?

I haven't received his letter yet.

Have you had your meal yet?

Have you eaten?

Just is only used in declarative sentences, which means: just now, it was placed after have and has. Example:

I just got a letter. ?

I have just received a letter.

Never is used in negative sentences: after never, have and has. Example:

I've never been there? Beijing. ?

I have never been to Beijing.

Ever is used in interrogative sentences, translated as "once, after have and has" example:

Have you ever been to Beijing?

Have you ever been to Beijing?

Before is used in affirmative sentences. In the past, it was placed after have and has, usually at the end of the sentence. Example:

He has never been to Beijing before. ?

He has never been to Beijing before.

7. Since the+continuation verb can be used in the simple past tense or the present perfect tense, it has different meanings: the simple past tense is used to indicate that the main sentence activity has continued since the sentence action "ended"; The present perfect tense is used to indicate that the main sentence activity has continued since the sentence action "started". Example:

I have worked in this company for three years. ?

I have not worked in this company for three years.

I have worked in this company for three years.

I have worked in this company for three years.