Change voice: She will have sung a song.

The original sentence, "She will have sung a song," is in the active voice, future perfect tense. To change it to the passive voice, we follow specific rules for this tense. The object of the active sentence ("a song") becomes the subject of the passive sentence. The auxiliary verb structure for future perfect passive is "will have been" followed by the past participle of the main verb ("sung"). The original subject ("she") becomes the object of the preposition "by." Therefore, Option A, "A song will have been sung by her," correctly applies these rules.

• Option B, "A song have been sung by her," is incorrect because it omits "will."
• Option C, "A song will had sung by her," is incorrect because "had" is past perfect, not future perfect passive.
• Option D, "A song has sung by her," is incorrect as it uses present perfect tense.

Mastering the specific auxiliary verb structures for each tense in passive voice is crucial for accurate voice transformation.