Choose the correct answer

Why does the plural masculine form لَيَفْعَلُنَّ have a Dhummah (پیش) on the letter before the Heavy Noon?

Structural Rules of Heavy and Light Noon-e-Ta'keed

• Because it is the default state of the verb
• To indicate that the subject pronoun Waaw was dropped
• Because of the prefix Laam
• Due to a random phonetic shift