Which statement best describes a keystone species? A. It has little genetic variation
B. It has an extremely high population
C. It remains unaffected by all environmental changes
D. It has a strong influence on the ecosystem
E. It's the first species to populate a new ecosystem

The gene that causes sickle-cell disease is present in a higher percentage of residents of sub-saharan africa than among those of african descent living in the united states. even though this gene causes sickle-cell disease, it also provides some protection from malaria, a serious disease that is widespread in sub-saharan africa but absent in the united states. discuss an evolutionary process that could account for the different percentages of the sickle-cell gene among residents of the two regions.

Iwill mark brainliest and all that sha-bang. what is the function of the endocrine system? a. control longer term response in the body. b. transmit messages throughout the body. c. remove waste from the body. d. all of the above

Cpr, or cardiopulmonary resuscitation, is a first-aid technique to save lives. it involves compressions of the patient's chest cavity. which description is the best description of the functions of chest compressions in cpr? chest compressions are done to pump the heart. chest compressions are done to strengthen the rib bones. chest compressions increase carbon dioxide inhalation. chest compressions allow the patient's muscles to wake up.