Answer: A
C2: priorities OH>CX1 (attached to C,C,C) >CX3 (attached to C,H,H) >H; the drawn arrangement gives (S). C1: its three ring neighbours are C2 (O,C,H), C6 (C,H,H) and C7 (C,H,H); C2 is first, and C6 versus C7 is decided at the next sphere (C6 leads to C5 which bears C4, while C7 leads directly to C4, whose set (C,C,H) beats the (C,H,H) of C5), so the order is CX2>CX7>CX6>H, giving (S). C4 with CX3>CX7>CX5>H gives (R). The compound shown is (1S,2S,4R); option B is its enantiomer.