Why it is neccessary to use Present Perfect Continuous not Present Perfect in the sentence below?
TB: It sounds like a very busy day.
MR: Oh, that's only part of it. I have had two meetings, one with Union representatives and one with departmental heads. And I HAVE ALSO BEEN WORKING on a proposal for a new marketing strategy.
TB: And it's not two o'clock yet.
If I say "And I HAVE ALSO WORKED" that's a mistake, so why Present Perf. Cont.?