We heard him asseverate his good intentions but his actions belied his words.

Answer: Option A

Affirm : state emphatically or publicly.
Incite : encourage or stir up (violent or unlawful behaviour).
Defy : openly resist or refuse to obey.
Cancel : decide or announce that (a planned event) will not take place.
Asseverate : declare or state solemnly or emphatically.

Synonym of Asseverate is Affirm