Step 1: Identify who or what is performing the action. The subject is 'the homework'. Homework cannot complete itself — it is the object that receives the action. This signals a passive voice construction is needed. Step 2: Form the passive voice. Passive voice = 'was/were' + past participle. The past participle of 'complete' is 'completed'. Step 3: Check the tense. The sentence is in the past ('before the teacher collected it'), so 'was' (not 'is') is correct. Answer: was completed