What are the limits to natural selection?

1.a change in environmental conditions , which can lead to such an adaption only for genetic trials already present in a populations genepool , or for traits resulting from mutations

2.heredity

3.Reproduction

variations in physical characters

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.

there's the proffessional site that will you.