The correct answer is (D) has won.
"Our school's chess team has won the interschool chess championship."
The sentence describes a recent event with a current relevance (a victory just announced), so the Present Perfect tense (has/have + past participle) is correct. Option A ("has been won") is passive and awkward here. Option B ("will winning") is grammatically incorrect. Option C ("was winning") implies an ongoing past action, not a completed one.