The intermolecular forces from strongest to weakest are ionic, hydrogen bonding, dipole-dipole, then London dispersion forces. All compounds experience some form of London dispersion force, but the force only becomes relevant if no other forces are contributing to the attraction of molecules or atoms.

Ethanol will not form ions in solution, so we are left with the other three options as plausible answers. Of the three, the strongest force is hydrogen bonding, which only occurs if a hydrogen is directly attached to a nitrogen, oxygen, or fluorine in the molecule. Ethanol has a hydrogen attached to an oxygen, and is thus capable of hydrogen bonding.