De or het conversielening?

The correct Dutch article is:

de conversielening

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

How to use conversielening

the conversieleningde conversielening
this conversieleningdeze conversielening
that conversieleningdie conversielening
our conversieleningonze conversielening
your conversieleningjouw conversielening
every conversieleningelke conversielening
which conversielening?welke conversielening?
a big conversielening / the big conversieleningeen grote conversielening, de grote conversielening