BC + CD = BD is the answer. the segment addition postulate basically just adds a whole segment together, but it's split into two parts.
B is the starting point, D is the endpoint, and C is somewhere in the middle. the rest of the answer choices don't describe segments that can use this postulate
basically all you were looking for is that the first letter and last letter of the added segments were in the answer and (B)C + C(D) = (BD) does that for ya
