Answer : 1. "The work will be completed by tomorrow."
Explanation :

In passive voice, the object of the active sentence (in this case, "the work") becomes the subject, and the active verb ("complete") is changed to its passive form ("completed"). The subject of the active sentence ("They") is either omitted or mentioned at the end with "by" followed by the doer of the action (optional in this case).

So, the transformation from active voice to passive voice is:

• Active voice: They will complete the work by tomorrow.
• Passive voice: The work will be completed by tomorrow.

This maintains the meaning of the original sentence while changing its grammatical structure to passive voice.