De or het startinvestering?

The correct Dutch article is:

de startinvestering

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

How to use startinvestering

the startinvesteringde startinvestering
this startinvesteringdeze startinvestering
that startinvesteringdie startinvestering
our startinvesteringonze startinvestering
your startinvesteringjouw startinvestering
every startinvesteringelke startinvestering
which startinvestering?welke startinvestering?
a big startinvestering / the big startinvesteringeen grote startinvestering, de grote startinvestering