）​staircase是on the staircase还是in the staircase还是at the staircase?

）​staircase是on the staircase还是in the staircase还是at the staircase?
）​staircase是on the staircase还是in the staircase还是at the staircase?

）​staircase是on the staircase还是in the staircase还是at the staircase?
in指在什么里面,或者指在某个大地方,如I‘m in Hainan,at Haikou
at指在一个小地方.
on指贴着表面的在.上面.
所以这里用ON