Answer:
The revision which changes the sentence from the passive voice to the active is the following one:
They sang the newly composed songs.
Step-by-step explanation:
In passive voice, the verb to sing is in past participle (sung), since it appears right after verb to be (were), indicating a passive action.
In active voice, the verb goes to simple past. The reason for it is that the in the passive voice, verb to be was in simple past as well (were):
passive voice: were sung → active voice: sang
Because the agent in the passive voice is "them" (introduced by the preposition "by", which indicates authorship), the subject or doer of the action in the active voice is "they":
passive voice: object pronoun "them" → active voice: subject pronoun "they"
Plus, there is a complete change in the order of the sentence and its elements when converting from the passive to the active voice:
The newly composed songs were sung by them. (passive voice)
↓
They sang the newly composed songs. (active voice)