El pretérito perfecto continuo está formado por el pretérito perfecto del verbo to be + el participio de presente:
Afirmativa: I have been working, he has been working etc.
Negativa: I have not/haven’t been working etc.
Interrogativa: have I been working? etc.
Interrogativa negativa: have I not/haven’t I been working?
A Practical English Grammar (A.J. Thomson & A.V. Martinet) 