根据句意和首字母提示完成句中所缺的单词。

1. My father and mother are my p _________.        

2. My father's brother is my u _________ .       

3. My mother's sister is my a __________ .        

4. My mother's mother is my g  _________ .      

5. My father's father is my g  _________.

试分析不对称信息形成的原因。