The question is about translation techniques. When converting a passive voice sentence into an active voice sentence, a common technique is to omit the agent (the noun that is performing the action) if it is not important or already known, which is answer A. Changing the tense (B) is not a common technique for this conversion. Adding a modal verb (C) is not related to this conversion, and using a reflexive pronoun (D) is also not a common technique for this purpose.