Rule reminder
'Dire' = to say (neutral, all-purpose). 'Affermare' = to affirm/state (formal, implies certainty). 'Dichiarare' = to declare (official, public statement). 'Sostenere' = to maintain/argue (implies defending a position under challenge). 'Asserire' = to assert (very formal, literary; strongest assertion of truth).
"Ciao, come stai?" — Non sapevo cosa _____.