Do you know the boy in the picture? He is Yi Yangqianxi. His English name is Jackson. Yi is 15 years old. He is a student in a school in Beijing. And he is also a boy in the group (组合) TFBOYS.

    TFBOYS has three boys — Wang Yuan, Wang Junkai and Yi Yangqianxi. All of them are tall and have good looks. They are good at dancing and singing.

    Wang Yuan and Wang Junkai are Yi's friends. And Yi has another (另一个) friend. He is a toy bear. He lives in Yi's schoolbag. Yi goes to school with him every day. He talks and plays with him. “He can't talk, but he can listen to me. He is very nice. I like him very much,” Yi says. “I don't want to be away from him.”

已知氨气分子和甲烷分子的空间构型分别为三角锥形和正四面体，造成这一差异的主要原因是   （      ）

读图并结合所学知识，西汉和秦朝相比，中央权力机构最大的变化是（    ）