De or het lustrumviering?

The correct Dutch article is:

de lustrumviering

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

How to use lustrumviering

the lustrumvieringde lustrumviering
this lustrumvieringdeze lustrumviering
that lustrumvieringdie lustrumviering
our lustrumvieringonze lustrumviering
your lustrumvieringjouw lustrumviering
every lustrumvieringelke lustrumviering
which lustrumviering?welke lustrumviering?
a big lustrumviering / the big lustrumvieringeen grote lustrumviering, de grote lustrumviering