Suppose you are Dean of Computer Science Department, Beijing University and you have taught Wu Dong for four years. Write a letter of recommendation for Wu Dong to: (1) state your relationship with him, (2) introduce his academic achievements, (3) introduce his language proficiency, (4) introduce his sports and social activities, and (5) express your sincere recommendation. You should write approximately 100 words. Do not sign your own name at the end of the letter. Use "Wang Lin" instead. You do not need to write the address.