Red hair may have evolved in the neanderthals and then was introduced into human populations via interbreeding. if this is true this would be an example of

Gene flow

If this is true, this would be an example of gene flow.

Gene flow is the movement of genetic materials or organisms from one population to another, thereby influencing the composition of the set of genes of the affected population. Gene flow usually occurs among humans through the relocation of human populations either willingly or not.

i think a) betsy can donate only blood to mark is correct because, mark and betsy have the same blood type. whereas nobody else has b+ blood so betsy can't donate to them.