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
在一高度处同时释放一片羽毛和一个玻璃球,玻璃球先于羽毛到达地面,其最根本的原因是因为( )
8+1=____