Hi Noemi, In your sentence, you started working on your project in the past (since Monday). It seems that you are still in the midst of doing it. For an action that commenced in the past, took place for a period of time and is still ongoing at the present, we use present perfect continuous tense. Present perfect tense is constructed using "has/have been" with "verb-ing". Hence, it would be "have been working ". Hope this helps. Cheers, Lance

It would be sad if you were trying to do the test at Italki experts' expense. :(

have been working.