Present perfect progressive

Al and Ann are in their car right now. They are driving home. It is now four o'clock
(a) They have been driving since two o'clock
(b) They have been driving for two hours. They will be home soon.
The Present Perfect Progressive talks about how long an activity has been in progress before now.
Note: Time expression with since, as in (a), and for as in (b), are frequently ued with this tense. Statement: have/has+been+-ing
(c) How long have they been driving?
Question form: have/has+subject+been+-ing
Compare the present progressive and the present perfect progressive
Present progressive
(d) Po is sitting in class right now
The Preent Progressive describes an activity that is in progress right now, ax in (d). It does not discuss duration (length of time).
Incorrect: Po has been sitting in class right now.
Present perfect progressive
Po is sitting at his desk in class. He sat down at nine o'clock. It is now nine-thirty
(e) Po has been sitting in class since nine o'clock
(f) Po has been sitting in class for thirty minutes.
The Present Perfect Progressive expresses the duration (length of time) of an activity that began in the past and is in progress right now.
Incorrect: Po is sitging in class since nine o'clock
(g) Correct: I know Yoko
(h) Incorrect: I am knowing Yoko
(i) Correct: I have known Yoko for two years
(j) Incorrect: I have been knowing Yoko for two years
Reminder: Non-action verbs (e.g, know, like, own, belong) are not used in any progressive tenses.
In (i): With non-action verbs, the present perfect is used with since or for to express the duration of a situation that began in the padt and continues to the present.
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