答案：D

had better相当于一个助动词,它的后面要跟动词原形；had better的否定式是将否定副词not直接放在had better的后面。如：You had better not miss the last bus.你最好不要错过末班公共汽车。否定副词not绝不能放在had的后面。如：不能说：You hadn’t better go.而应该说：You had better not go.故选D。