问题补充：
Disthinguished guests and friends, welcome to our school! the ceremony of the 50th anniversary this morning are our alumni (校友) from home and abroad.
A. Attend
B. To attend
C. Attending
D. Having attended
答案：
A. Attend
B. To attend
(答案→)C. Attending
D. Having attended
解析：可联系答.案.网客服索取。
