Dear David:
I am sorry to hear of(去掉of) that you couldn't（didn't) pass that(the) examination.I know you should(might) be frustrated now. As your friend ,I want(would like) you to know that once（one) failure dosen't（doesn't) mean anything. You need to put yourself together (and) get back to (prepare) for the next examination.You could came(come) to me for help, if you might(去掉） have any questions where(which) you don't understand. Don't be shy. and remember we are friends.I wish you can(could)
catch up with your classmate(classmates) through your hard study.
your sincere friend Martin