The politicians have been discussing the social program for the last month. Are discussing is present continuous, have discussed is present perfect, discuss is present simple.
The present perfect progressive form of the verb <em>discuss</em> that completes the sentence is "have been discussing.
Explanation:
The present perfect progressive tense is used to talk about a continous action that has been finished at some point in the past or that was initated in the past and continues to happen. This tense is formed with the auxiliary verb HAVE/HAS plus BEEN and the present participle of the main verb (-ing).
