Dear (后跟老师名字),
I feel deeply sorry that I did not attend the last English class. I took part in an importantDebating Contest, and the time was just the same with the English lesson. If I miss this contest, Ilose a wonderful chance in my life; if i miss the English lesson for only once and temporarily, I could make up. You have been always telling us to grasp every chance in our lives; I believe it is right. This time I choose to take part in the contest. That is why I did not attent the english class last week, and I hope you could understand. I promise I will make up for my absence.
Yours(后跟自己的名字,此句应在右侧,百度不容易调整,你用的时候自己调吧)