Hey guys i'm back and i'm having trouble here

Which of the following examples can cause gene flow between populations? a.an increase in predators to a population of zebra b.a volcanic eruption that kills half of a population of mice c.bird droppings that contain seeds from a different location d.a person that sprays a toxin on a group of mosquitoes

As a small change in a person's dna can cause a genetic disorder

Which was most likely an effect on society that resulted from improvements in blood handling during world war i and world war ii?