8. 的命名為 (A) (2R,4S)-5-Mercapto-4-methylpentan-2-ol (B) (2R,4R)-5-Mercapto-4-methylpentan-2-ol (C) (2R,4R)-4-hydroxy-2-methylpentane-1-thiol (D) (2R,4R)-5-thiol-4-methylpentan-2-ol