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Why do the two plural feminine forms يَفْعُلْنَ and تَفْعُلْنَ NOT change at all when prefixed with لَنْ?

Rule of Emphatic Negation in Future with "Lan" (لَنْ)

• Because their ending Noon is a subject pronoun and is indeclinable (مبنی)
• Because they are past tense forms
• Due to a print mistake in the book
• Because they do not have any vowels