Which of the following is a characteristic of 'Context-Free Grammars' (CFG) in computational linguistics?

1. ক
   They can describe all natural language phenomena perfectly
   
2. খ
   They use production rules where a single non-terminal is replaced by a string of terminals/non-terminals
   
3. গ
   They are equivalent to Finite State Automata
   
4. ঘ
   They require infinite memory for processing