It is quite ____ that they live in ______ building in the st

It is quite ____ that they live in ______ building in the street.
It is quite _____ that they live in _____ building in the street.
A sure/a B sure/certain C certain/certain D certain/some
这句话我理解的意思是,很确定,他们住在这条街上的某个大楼里.
我知道答案是选择CERTAIN/SOME,如果AB选项的后一个选项变成some ,那么AB也可以选择是吗?
但是我觉得 A 选项的in a building 貌似也没有错误啊!
然后这里的some 是指某个的意思,而不是一些的意思吗?所以不用building 不用加s吗?