Correct Answer: The assignment must be completed by the students by Friday.

Solution : The first option is the correct answer.

Passive voice is the voice in which the object experiences an action rather than the person who performs the action. Hence, the object in the active sentence becomes the subject in the passive voice.

The passive voice structure in the case of sentences with modals generally follows the pattern: "Object + auxiliary verb + be + past participle form of the main verb + by + agent (optional)."

Therefore, the correct answer is: "The assignment must be completed by the students by Friday."