Wrong evidence. The evidence indicates the joke was not contemptuous. And, although it indicates that the joke would bring significant harm to “someone” — we don’t know that the “someone” is the person on whom the joke was played. In addition, (A) acknowledges that the author “should have realized” that the joke would harm someone, but that doesn’t establish the author actually believed that it might harm someone before the joke was played.

Unreachable conclusion. (B) concludes that playing a practical joke was “not wrong” (or in other words, that it was OK to play the joke). But the principle allows us to conclude when one should NOT play a practical joke. It doesn’t allow us to conclude when it’s acceptable to play a practical joke. (If you think it does, you’re confusing sufficient and necessary conditions).

Correct, because it validly uses the principle. The evidence in (C) establish that the author knows the joke “could easily bring you significant harm.” Using the principle, we can then conclude that the author should not play the joke on you.

Wrong evidence. The premises do not establish that the joke showed contempt for the person who was the victim of the joke. It establishes only that the joke would show contempt for “someone”; we don’t know whether that person was the victim of the joke. Also, the evidence does not establish that the author believed the joke might harm the victim of the joke.

Wrong evidence. The evidence does not establish that the joke showed contempt for the victim of the joke, or that the author believed that the victim of the joke might be harmed.