Present Perfect Continuous

1. अगर कोई कार्य past में शुरु हुआ हो और अभी तक चल रहा हो तो verb form present perfect continuos में होता है। ऐसी स्थिति प्रायः since + point of time तथा for + period of time के साथ स्वाभाविक है।
For example:
(a) The meeting had already being going on, when I reached there.
(b) He must be tired as he has been watching television since morning.