Which term describes the sound change process where a sound is added to the middle of a word, such as 'hamster' from earlier 'hamster' variants or 'thunor' to 'thunder'?

1. ক
   Epenthesis
   
2. খ
   Metathesis
   
3. গ
   Apocope
   
4. ঘ
   Syncope