The correct answer is Option 3: Completed.

The sentence uses the present perfect tense, which indicates an action that began in the past and continues up to the present or has just been completed. The present perfect tense is formed with the auxiliary verb "have" or "has" followed by the past participle of the main verb.

In this case, the main verb is "complete," and its past participle is "completed." Therefore, the correct verb form to use is "completed."

Here is the complete sentence:

I have completed my homework just now.