To Geoffrey
I am _ from class _. My grades in _(不及格的课) is unsatisfactory. The subject code is _(课程编号). I heard that there will be a supplementary examination soon, so I am writing to enrol for a position in the exam. Thank you.
最后哪句话 用这个也可以：I heard that there will be a supplementary examination soon. I am writing to you in order to undertake the supplementary examination.