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

unless it is possible to determine the jury necessarily found the defendant guilty on a proper theory. As explained in People v. Perez (2005) 35 Cal.4th 1219, 1233, 29 Cal.Rptr.3d 423, 113 P.3d 100 ( Perez ), [w]hen one of the theories presented to a jury is legally inadequate, such as a theory which fails to come within the statutory definition of the crime [citations], the jury cannot reasonably be expected to divine its legal inadequacy. The jury may render a verdict on the basis of the legally invalid theory without realizing that, as a matter of law, its factual findings are insufficient to constitute the charged crime. In such circumstances, 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. [Citation.] ( Id. at p. 1233, 29 Cal.Rptr.3d 423, 113 P.3d 100.)