The area of land from which water drains into a river

Environmental differences within ecosystems are generally caused by

Explain how ancient whale fossils found in eqypt are believed to support the theory of evolution.

Vaccines are weakened forms of disease causing microorganisms, which are given to patients to prevent disease. after the vaccine is administered, the immune system responds by creating a(n) to recognize the a.) antibody, antibiotic b.) antigen, antibody c.)antibiotic, antibody d.)antibody, antigen