De or het subthema?

The correct Dutch article is:

de subthema

This word is not in the word lists we use to double-check answers.

How to use subthema

the subthemade subthema
this subthemadeze subthema
that subthemadie subthema
our subthemaonze subthema
your subthemajouw subthema
every subthemaelke subthema
which subthema?welke subthema?
a big subthema / the big subthemaeen grote subthema, de grote subthema