I am not quite clear about the use of the object case with the adjective forms of verbs. How about these sentences: "La finanta siajn studojn studento devis trinki multan kafon." "La hundo vidas la katon kaptantan muson."
They're not the same, but the present tense is used a lot in Esperanto where in English we would use the present progressive. You definitely could use the present tense here, and many Esperanto speakers would, but since this unit is teaching us about participles and complex verb forms, they want answers in the present progressive.