For a molecule to absorb IR, why must the molecule's vibrations cause fluctuations in the dipole moment of the molecule?

Question:For a molecule to absorb IR, why must the molecule's vibrations cause fluctuations in the dipole moment of the molecule?

1.Because a change in dipole moment lowers the energy required for electronic transitions

2.Because for absorption to occur, the radiation must interact with the electric field caused by changing dipole moment

3.Because fluctuations in the dipole moment allow the molecule to deform by bending and stretching

4.All of the above

Answer:2