Step 1: Identify the time relationship. The sentence contains two past events: (a) the poster was designed, and (b) the judges announced the results. Event (a) happened BEFORE event (b). Step 2: Choose the correct tense for the earlier event. When one past action is completed before another past action, use the past perfect: had + past participle. Step 3: Determine the voice. The subject 'the winning poster' receives the action of designing. Passive voice is needed: had been + past participle. Step 4: Form the verb phrase. Past perfect passive = 'had been' + past participle of 'design' = 'had been designed'. Answer: had been designed