Read these lines: "I must not only punish, but punish with impunity. A wrong is unredressed when retribution overtakes its redresser. It is equally unredressed when the avenger fails to make himself felt as such to him who has done the wrong." According to the quoted lines, the speaker's revenge must satisfy two conditions:

1. The first condition is stated in the opening sentence: he must punish with impunity, meaning without any penalty falling on himself. 2. The second sentence explains why, since a wrong is unredressed if punishment catches the one who takes revenge. 3. The third sentence adds the other half: the wrong is equally unredressed if the avenger fails to make himself felt as such to the wrongdoer. 4. So the victim must know who is doing this and why, which together with escaping penalty gives option A. 5. Option C sets a public act and a warning, both of which would destroy the first condition. _Source: Edgar Allan Poe, The Cask of Amontillado, public domain_