So compound D.
So now we have a ring, a compound, a ring structure. So let's begin labeling on this guy, on this carbon. So 123456. So once again, I begin labeling or numbering on my double bond because I want my double bond to have the lowest possible number value. So this guy is known as one cyclone because it's a cyclic compound, and we have six, so hexene. So one cyclohexine, or simply cyclohexine.