问几道高一的英语改错题,可我就不知到为什么答案会是这样

题目

问几道高一的英语改错题,可我就不知到为什么答案会是这样
south of the building are our palyground（把are改为is）
he is the first boy coming to school this morning（coming改为to come）
she was about saying something when her father came in（saying改为to say）

答案

1.south of the building 是方位名词,单数.
2.（to be)the first to do sth.第一个做……的人.
3.be about to do sth.将要做某事.