题干
In April, 2009, President Hu inspected the warships in Qingdao, ______ the 60th anniversary of the founding of the PLA Navy.
A：marking
B：marked
C：having marked
D：being marked
答案(点此获取答案解析）
A
是集合A到集合B的映射，如果B={1,2}，则
为 （ ）