Correct Answer:
A. My bag has been stolen
To convert an active voice sentence in the present perfect tense to passive voice, the structure changes from "has/have + past participle" to "has/have + been + past participle". In the active sentence, "my bag" is the object, and "has stolen" is the present perfect active verb. Therefore, in the passive voice, "my bag" becomes the subject, and the verb phrase becomes "has been stolen". Options B, C, and D do not follow the correct present perfect passive structure. "Had stolen" is past perfect active, "stole" is simple past active, and "is stolen" is simple present passive.