What is a criticism of the biological species concept?
a.) all of the answers are valid b.) it can not be applied to organisms that reproduce asexually, and to many plants which hybridize freely
c.) it can not be applied to organisms that cannot be easily studied in nature (for verification of RI) or to extinct organisms
d.) gene flow is notoriously difficult to investigate e.) it can be difficult to apply in practice, particularly in populations that are geographically isolated from one another