1. still是副词，不同类。其余两个都是形容词。

2. still的含义是: 仍然，仍旧，还。例句: She is still young even after twenty years has passed.尽管二十年过去，她还是那么年轻。

3. 其余两个都是形容词。

different 不同的。用法: be different from。His way of swimming is very different from that of his elder brother. 他与哥哥的游泳姿势很不相同。

enough充足的。We didn't have enough food those years. 那些年，我们没有足够的食物。