首先，and可以用来连接两个并列子句，前后两个句子的主语不必相同，例如： Rose likes to dance and her father likes to sing. 罗斯喜欢跳舞而她的父亲喜欢唱歌。 第二，你所举的例子与前面的问题无关。那是另一个概念。 The plane is at the airport,and it has been surrounded by police . 飞机在机场上，它已被警察包围了。 这是两个并列子句，主语都是plane，只不过第二句为避免重复，把plane改为it罢了。 The plane is at the airport,where it has been surrounded by police . 飞机在机场上，它已在机场被警察包围了。（飞机在它已被警察包围住的那个机场上。） 这是另一个讲法，是主句加上一个定语从句的结构，it has been surrounded by police 是一个定语从句，由where引导，修饰airport。 不一定啊 比如 I went to park last Saturday, and she went shopping on that day. and 是连词，连接两个句子或者两个短语的，如果是短语，有时候要求形式一致，比如 I wish I can work in a bank and make a lot of money. The plane is at the airport,___ it has been surrounded by police 这句之所以选where 是定语从句 airport是先行词 1. and可以用来连接两个并列子句，前后两个句子的主语不必相同. 2. 举例：i went to park last saturday, and she went shopping on that day. and 是连词，连接两个句子或者两个短语的，如果是短语，有时候要求形式一致，比如 i wish i can work in a bank and make a lot of money. 不是哦，用where是他引导了定从哦 主语前后可以一致也可不一致，不过前后后主语相同，后面的往往省略