Which of the following sentences are used for the opening of a recommendation letter?

A、I am writing this letter to recommend my student Wang Hua, who is seeking the position of marketing clerk of your company.
B、During the past three years, I have come to know Zhang Lin well and would like to recommend him as a candidate for your undergraduate program.
C、When he studied in our university, he passed all the courses with excellent math.
D、It is my hope that her application will be looked upon favorably.