What is the test for having a unanimous verdict in a criminal case?

Appellant claims his convictions must be reversed because the court failed to give a unanimity instruction. In a criminal case, a jury verdict must be unanimous, and the jury must agree unanimously that the defendant is guilty of a specific crime. (People v. Russo (2001) 25 Cal.4th 1124, 1132.) "[W]hen the evidence suggests more than one discrete crime, either the prosecution must elect among the crimes or the court must require the jury to agree on the same criminal act." (Ibid.)