B) decrease genetic diversity
Genetic Diversity refers to vast differences in genetic makeup (genotype) and thus often phenotype as well. The more that extreme genes/traits are excluded in survival and/or reproduction, leading to stabilizing selection, then the more genetically "same" or similar the population will evolve to long-term. Similarity is the opposite of diversity. Thus A) is dead wrong, B) is accurate, and both C) & D) are incorrect because "rare" means not common or "extreme." And extreme traits are exactly what decrease through stabilizing selection.
Hope that this.helps! :)
