12/2/2006 9:03:34 PM
12/2/2006 9:22:44 PM
suppose we have a river that we need to get people across regularlythe solution is a bridge, that bridge could be implemented by wooden planks, stone blocks, metal beams, or concrete
12/2/2006 9:29:05 PM
12/2/2006 11:05:32 PM
12/3/2006 12:11:40 AM