Correct Answer: A deep trench is being dug by the soldiers.

Solution : The second 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 structure of the passive voice for the present tense sentence is:

"Object  + is being + past participle of the main verb + by + agent of action"

Therefore, the correct answer is: "A deep trench is being dug by the soldiers."