One day my instructor told me that the thesis should be written fully in
English form,because he couldn't accept his student to write paper in Chinese.
It was really a sad thing to me,because I didn't improve my English during
college years even that I got 90 points at the JCEE and have certification of
GEPT. It was still a sad thing for me. I still need to learn more and improve
English writting ability instead of speaking Chinglish. I am not good at
English compared to Math. Hope that I can finish the paper by myself in the
future.

you dont add common in front of becausethere are really lots mistakes in ur writing.you need to find a instructor to correct for you

actually you can put comma before because, the rule"never put comma before because" is wrong

Thank you guys! I'll try hard.I don't really like English,andlearning other languagesmakes it worse.

Believe you will get improvement through practices.