de oplossing — solution
de oplossingen
Most Dutch nouns add -en (with a spelling tweak).
Every Dutch plural takes de. Check the singular article →
The plural (meervoud) of oplossing is "de oplossingen". Most Dutch nouns add -en (with a spelling tweak).
Like every Dutch plural, de oplossingen takes de. Dutch plurals are always de-words, regardless of the singular article.
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