Select all correct statements about how drugs bind their targets.

1. AHydrogen bonding and van der Waals forces give reversible binding.
2. BA drug covalently bound at an active site is not displaced by a large excess of substrate.
3. CIonic attraction and dipole-dipole forces are too weak to hold any drug on a target.
4. DIrreversible inhibition amounts to a chemical reaction between the drug and a residue of the target.