De or het museumsuppoost?

The correct Dutch article is:

de museumsuppoost

How to use museumsuppoost

the museumsuppoostde museumsuppoost
this museumsuppoostdeze museumsuppoost
that museumsuppoostdie museumsuppoost
our museumsuppoostonze museumsuppoost
your museumsuppoostjouw museumsuppoost
every museumsuppoostelke museumsuppoost
which museumsuppoost?welke museumsuppoost?
a big museumsuppoost / the big museumsuppoosteen grote museumsuppoost, de grote museumsuppoost