De or het theorieontwikkeling?

The correct Dutch article is:

de theorieontwikkeling

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

How to use theorieontwikkeling

the theorieontwikkelingde theorieontwikkeling
this theorieontwikkelingdeze theorieontwikkeling
that theorieontwikkelingdie theorieontwikkeling
our theorieontwikkelingonze theorieontwikkeling
your theorieontwikkelingjouw theorieontwikkeling
every theorieontwikkelingelke theorieontwikkeling
which theorieontwikkeling?welke theorieontwikkeling?
a big theorieontwikkeling / the big theorieontwikkelingeen grote theorieontwikkeling, de grote theorieontwikkeling