Which of these is an example of gene flow?

a) german immigrants settle in a colony in eastern pennsylvania without mixing with the locals.
b) a few black sparrows join a population of brown sparrows and mate with them.
c) indiscriminate hunting reduces the blue whale population, which later revives.

I think the correct  answer from the choices listed above is option A. An example of gene flow would be that German immigrants settle in a colony in Eastern Pennsylvania without mixing with the locals. Gene flow is the movement of individuals from one population to another. It is also called migration.