Thepoint is that using present perfect continuous in a sentence already shows that it is still taking place. and i learnt that we need to use 'ago' with few years, 10 years, etc to make it have a start and end but for present perfect continuous it has already an end ( still taking place) so that means we don't need to put 'ago' in the end?
Thebroad rule is that although both tenses relate to the fact that something is being referred to in the past, the present perfect refers to something that has finished, but the present perfect continuous refers to something that is continuing in the present. However, although this is sometimes the case, there are more variations. Forother uses of the Present Perfect tense, see the Present Perfect Tense - When To Use. We use for with a period of time, for example: a few days, half an hour, two years. We use since with the time when the action started, for example: last year, June 8, I met you. QuickExercise. Complete the following sentences using the present perfect continuous tense form of the verbs in brackets. 1. Mrs. Rose (teach) English for ten years. 2. Her grandma (talk) for three hours. 3. A little boy (stand) at the door since noon.