A:to working
B:to work
C:to have worked
D:working
用棋子摆出下列一组图形:
按照这种规律摆下去,第n个图形用的棋子个数为( )
如图,△ABD是等腰三角形,AB=AD,将△ABD沿BD翻折得△CBD,点P是线段BD上一点,