请帮忙检查一下英语语法错误This thesis consists of three parts: the first one is the introduction, this part is mainly introduces the development and significance of the positive definite matrix.

This thesis consists of three parts: the first one is the introduction, this part is mainly introduces the development and significance of the positive definite matrix.
1 如果用冒号的话，就得把三个部分全列出来
2 introduction后面是另一句话，用句号隔开
3 有is就不要加动词，有动词就不要用is
完整: This thesis consists of three parts, and the first one is the introduction. This part introduces the development and significance of the positivedefinite matrix.

This thesis consists of three parts: the first one is the
introduction, WHICH mainly introduces the development and significance of
the positive definite matrix.