What is the primary focus of 'Interlanguage' in Second Language Acquisition?

1. ক
   The native language of the learner
   
2. খ
   The linguistic system developed by a learner that is distinct from both L1 and L2
   
3. গ
   The final proficiency level of a bilingual speaker
   
4. ঘ
   The translation method used in classrooms