de periode — period
de periodes
Nouns ending in -e usually add -n (gedachte → gedachten).
Every Dutch plural takes de. Check the singular article →
The plural (meervoud) of periode is "de periodes". Nouns ending in -e usually add -n (gedachte → gedachten).
Like every Dutch plural, de periodes takes de. Dutch plurals are always de-words, regardless of the singular article.
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