单项选择题

Questions 162-164 refer to the following letter.
LA Music Academy
370 South Fair Oaks Ave, Pasadena, California 91105
Phone: (626) 568-8150
September 1
Dear colleagues,
I am writing to let you know that I have accepted a position as a music director of the Oregon Symphony and will be resigning from my position as a senior lecturer here on September 22. The decision to leave LA Music Academy has been an extremely difficult one, as I have enjoyed teaching at our school tremendously.
However, I do feel that it is time for me to move on to the next stage of my musical career. I believe the position at Oregon provides an opportunity for such growth.
During my seven years at this academy, I have had the privilege of working with many fine musicians such as yourselves. I am very grateful for your hard work and encouragement and wish you continued success.
Best wishes,
Phillip Janssen
What is the main purpose of this letter

A. To recommend a staff member
B. To describe a collaboration
C. To announce a resignation
D. To state a job description