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bold= my corrections/ suggestions

strikethrough= unneccessary 

One of my best friends is called jinjia. She is a very optimistic and funny person. She is kind to me and we get along well with each other. She was born into a big family as the youngest child because she and has three brothers and one sister, and she is the youngest child in her family. But her two brothers don't care about her old parents, so she is very annoyed. And Now she still study studies at school so that she can take care of her parents when she grows up. , she said when she grow up, she will take care of her parents patiently. I totally agree with her and I trust her because she is determined/hard-working. Nothing is more important than our parents. They gave us birth to us, so we should appreciate them. I love my parents very much, and nothing can replace them in my heart.

Final Version: 

One of my best friends is Jinjia. She is a very optimistic and funny person. She is kind to me and we get along well. She was born into a big family as the youngest child and has three brothers and one sister. But her two brothers don't care about her old parents, so she is very annoyed. Now she studies at school so that she can take care of her parents when she grows up. I totally agree with her and I trust her because she is determined/hard-working. Nothing is more important than our parents. They gave birth to us, so we should appreciate them. I love my parents very much, and nothing can replace them in my heart. 

I agree! We should cherish our parents. Nice job!