20. Maxwell added the concept of displacement curtent into Ampere's law, thereby completing the theory of electromagnetic waves. This modification suggests that equivalent currents can exist even in the absence of real currents under certain circumstances. The modified Maxwell's equations indicate: (A) Static magnetic fields can generate static electric fields. (B) Changing electric fields produce magnetic fields. (C) Static electric fields can generate static magnetic fields. (D) Blectric and magnetic fields are completely independent and do not generate each other. (E) Changing magnetic fields do not produce electric fields.