Question 1: The factors that change the gene frequency of the population are mobility and natural selection. Gene mutation is generally not considered. But variation is the raw material of biological evolution, including gene mutation and chromosome variation. When the gene frequency of a population changes, the population evolves. The second question: I think the "necessary condition" in option C is a mathematical and logical relationship. The explanation is that the formation of new species does not have to be isolated, but isolation can indeed form new species. Corresponding to it are "sufficient conditions" and "necessary and sufficient conditions". The first half sentence of option C can also be changed to: "The formation of new species is a sufficient condition for isolation." (regardless of the relationship between conditions and conclusions)