What is the legal test for reversal of a jury verdict in a sexual assault case?

When a jury is presented with a legally invalid theory to support a charge, such as a theory which "'"fails to come within the statutory definition of the crime"'" reversal generally is required unless "'it is possible to determine from other portions of the verdict that the jury necessarily found the defendant guilty on a proper theory.'" (People v. Perez (2005) 35 Cal.4th 1219, 1233, quoting People v. Guiton (1993) 4 Cal.4th 1116,

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1128, 1130.) "Trial courts have the duty to screen out invalid theories of conviction, either by appropriate instruction or by not presenting them to the jury in the first place." (People v. Guiton, supra, at p. 1131.) When, however, the court's instructions correctly state the law, but the prosecutor arguably misstates the law during closing argument, the error is prosecutorial error only, not trial court or instructional error, and the defense forfeits the claim of prosecutorial error on appeal unless it timely objects to the error in the trial court. (See People v. Morales (2001) 25 Cal.4th 34, 43-44.)