桌子上有3张“红桃”、7张“黑桃”和4张“方块”。这14张牌都背面向上放在桌上，从中至少取出（ ）张牌，才能保证一定有2张“黑桃”。
9
The famous writer and editor of the newspaper as well as many reporters _________ to the quake-hit
villages to cover the post-quake relief.[ ]
A. has been sent
B. have sent
C. has sent
D. have been sent
如图所示，在斜面顶端a处以大小为va的水平速度抛出一小球，经过时间ta恰好落在斜面底端P处；今在P点正上方与a等高的b处以大小为vb的水平速度抛出另一小球，经过时间tb恰好落在斜面的中点处．若不计空气阻力，下列关系式正确的是（ ）
A．va=vb
B．va=2vb
C．ta=tb
D．ta=2tb
