De or het tunnelverbinding?

The correct Dutch article is:

de tunnelverbinding

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

How to use tunnelverbinding

the tunnelverbindingde tunnelverbinding
this tunnelverbindingdeze tunnelverbinding
that tunnelverbindingdie tunnelverbinding
our tunnelverbindingonze tunnelverbinding
your tunnelverbindingjouw tunnelverbinding
every tunnelverbindingelke tunnelverbinding
which tunnelverbinding?welke tunnelverbinding?
a big tunnelverbinding / the big tunnelverbindingeen grote tunnelverbinding, de grote tunnelverbinding