Acid etching of dentin with 10-15% phosphoric acid for 15-20 seconds
1. removes the smear layer.
2. increases dentinal permeability.
3. opens the dentinal tubules.
4. decalcifies the intertubular and peritubular dentin

(1) and (3)

All of the above

(1) (2) (3)

(4) only

(2) and (4)