Could be false. We know that all monsters that are horrific are threatening. This doesn’t mean every monster that’s threatening is horrific. There can be threatening monsters that aren’t horrific (maybe they’re threatening for some other reason).

Could be false. We know that monsters that inspire revulsion are horrific. That doesn’t imply monsters that don’t inspire revulsion are not horrific. They can still be horrific for other reasons besides revulsion.

Could be false. We know that physically dangerous monsters are threatening. We also know that horrific monsters are threatening. This doesn’t imply that monsters that aren’t physically dangerous aren’t horrific. A monster can be horrific without being physically dangerous.

Could be false. We know that monsters that inspire revulsion are horrific. This doesn’t imply that monsters that are horrific don’t inspire revulsion. It’s possible every monster that’s horrific and threatening inspires revulsion.

Must be true. The stimulus tells us that all monsters that inspire revulsion are horrific, and all monsters that are horrific are threatening. So, all monsters that inspire revulsion are threatening.