42 牙科長石系陶瓷(feldspathic porcelain)中,為調整熱膨脹係數與燒附的金屬相近,常添加何種成分? (A)白榴石(leucite) (B)氧化硼(boric oxide) (C)高嶺土(kaolin) (D)石英(quartz)