De or het fusieonderneming?

The correct Dutch article is:

de fusieonderneming

Rule Words ending in -ing: almost always de. See the rule

How to use fusieonderneming

the fusieondernemingde fusieonderneming
this fusieondernemingdeze fusieonderneming
that fusieondernemingdie fusieonderneming
our fusieondernemingonze fusieonderneming
your fusieondernemingjouw fusieonderneming
every fusieondernemingelke fusieonderneming
which fusieonderneming?welke fusieonderneming?
a big fusieonderneming / the big fusieondernemingeen grote fusieonderneming, de grote fusieonderneming