根据句子意思及首字母提示完成单词。

1. Candy is her favourite food, but it isn't h _____ food.

2. Daming can play table tennis but he can't play the p_____.

3. My parents live in Beijing. I often s_____ emails to them.

4. Tom usually plays basketball but he n_____ plays computer games.

5. We can download music from the I_____.

线形缩聚的核心问题是（）；体形缩聚的关键问题是（）。所有缩聚反应共有的特征是（）