Hi Shirnel, I'm not sure exactly what your question is here but lets run through the question really quick. If we lay out our conditionals and their contrapositives: P1) Not C -> A // Not A -> C P2) D -> Not B // B -> Not D Missing Premise) Conclusion) D -> A // Not A -> Not D
So if we want to get to starting point D ending in A, we have D -> Not B starting with D and we have Not C -> A ending in A. If we connect these with a missing premise of Not B -> Not C we get D -> Not B -> Not C -> A Or simplified to D -> A. This is exactly what we want so our missing premise is Not B -> Not C We can also write this as the contrapositive C -> B
Since Not B -> Not C // C -> B are logically equivalent, either of them is correct but we'd choose C -> B since that's the one our answer options are giving us. Feel free to follow up if this doesn't answer your question.
