Answer:
When they've arrived in Cyprus, Iago sets his machinations to motion. He tricks Cassio into getting drunk, then has Roderigo—a former suitor of Desdemona whom Iago has convinced to aid him with the hope of winning Desdemona back—pick a fight with Cassio that ends in Cassio's arrest. Because of this, Cassio is demoted.
Step-by-step explanation: