【答案】：
1-Summer. 2-Because I can swim in the river. 3-No, I don't. 4-I like to make snowmen. 5-You learn fast.
【解析】：
1. "What's your favourite season?"询问最喜欢的季节，答语应为季节名称，故连"Summer."。
2. "Why do you like summer?"用Why提问原因，答语用Because开头，故连"Because I can swim in the river."。
3. "Do you like to run in winter?"是一般疑问句，答语用Yes/No回答，故连"No, I don't."。
4. "What do you like to do in winter?"询问冬天喜欢做的事，答语为具体活动，故连"I like to make snowmen."。
5. "How did I do?"询问做得怎么样，答语" You learn fast."符合语境。
