The diagram shows some cubes of the same size stacked at a corner of a room. How many cubes are there altogether? (Note: The floor is horizontal and the two walls are vertical. There are no gaps or holes behind the visible cubes). 
选项为:A:$$24$$  B:$$25$$  C:$$26$$  D:$$27$$  E:$$28$$  请回答其中一个选项.