De or het themacommissie?

The correct Dutch article is:

de themacommissie

Rule Words ending in -tie and -sie: almost always de. See the rule

How to use themacommissie

the themacommissiede themacommissie
this themacommissiedeze themacommissie
that themacommissiedie themacommissie
our themacommissieonze themacommissie
your themacommissiejouw themacommissie
every themacommissieelke themacommissie
which themacommissie?welke themacommissie?
a big themacommissie / the big themacommissieeen grote themacommissie, de grote themacommissie