What is the 'Affective Filter' in Krashen's theory of second language acquisition?

1. ক
   A mental block caused by anxiety, low self-esteem, or lack of motivation
   
2. খ
   A grammatical rule that filters out incorrect verb forms
   
3. গ
   The physical ability to hear sounds clearly
   
4. ঘ
   The process of translating thoughts into a target language