单选题 The dentist had to remove two teeth because they were decaying.
【正确答案】 A
【答案解析】go bad：变坏，变糟；destroy：毁坏，毁灭；go to pieces：瓦解；rotten：腐烂的，腐朽的。题中decay意为“渐渐衰落，衰变”，故选A。