A learner changes هُنَّ يَكْتُبْنَ to لَمْ يَكْتُبُوا. What is the error?

Mudari Akhaff and Lam

• The feminine-plural form was wrongly changed into the masculine plural
• The final dammah was not changed to fatḥah
• The interrogative hamzah is missing
• The verb should have become singular