What is the test for a jury to acquit a jury in a first degree murder case where there is insufficient evidence to support one of the two theories?

Generally speaking, "[w]hen a jury is instructed on two theories of first degree murder, a first degree murder verdict will be upheld [even] if there is insufficient evidence as to one of the theories." ( People v. Sandoval (2015) 62 Cal.4th 394, 424, 196 Cal.Rptr.3d 424, 363 P.3d 41.) In such cases, where "the inadequacy of proof" as to one of the theories of first degree murder is "purely factual," it is presumed that the jury is "fully equipped to detect" the deficiency and must have relied on the other, factually valid theory. ( People v. Guiton (1993) 4 Cal.4th 1116, 1129, 17 Cal.Rptr.2d 365, 847 P.2d 45.)