Answer:
That Cassio and Desdemona have an affair
Step-by-step explanation:
In his soliloquy at the end of Act I, Scene 3, Iago pretends to use Cassio to hurt Othello. By inciting Othello's jealousy through the idea that Desdemona and Cassio are having an affair. Iago thinks that because Cassio is good-looking, Othello will easily believe that Desdemona has been seduced by him. Iagotakes advantage on Othello's ingenuousness