This is not supported. The stimulus says that mystery stories “often” feature such a detective, but that’s not enough to be certain that “most” mystery stories use this technique.

This is not supported. The facts above don’t explain how readers go about solving the mystery in a story. All we know is that it’s sometimes possible for them to do so, which does not support concluding that they use this particular strategy.

This is strongly supported. The stimulus says that some mystery stories give readers a chance to solve the mystery by including a dull companion. So, the stories must contain enough clues for the reader to infer the solution, or else they wouldn’t actually have a chance.

This is not supported. We don’t know from the stimulus how much attention readers typically give to either the detective or the companion in mystery stories, so we can’t say if one does or doesn’t divert from the other.

This is not supported. The stimulus doesn’t indicate where the clues in mystery novels usually come from, or who uncovers them. We don’t know if it’s the companion, the detective, or someone else.