need help explaining asap please :(

Different types of selection may occur within a species in response to environmental change. Which of the following would provide evidence that stabilizing selection is occurring in response to environmental conditions?

A shift in a population's frequency curve from an intermediate phenotype to an extreme phenotype
A shift toward equal distribution of all phenotype frequencies, including intermediate and extreme phenotypes
An increase in the frequency of extreme phenotypes and a decrease in the frequency of intermediate phenotypes
An increase in the frequency of intermediate phenotypes and a decrease in the frequency of extreme phenotypes