De or het mega-investering?

The correct Dutch article is:

de mega-investering

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

How to use mega-investering

the mega-investeringde mega-investering
this mega-investeringdeze mega-investering
that mega-investeringdie mega-investering
our mega-investeringonze mega-investering
your mega-investeringjouw mega-investering
every mega-investeringelke mega-investering
which mega-investering?welke mega-investering?
a big mega-investering / the big mega-investeringeen grote mega-investering, de grote mega-investering