Which of the Following Factors Is Significant in Setting the Present

Which of the following factors is significant in setting the present carrying capacity of Earth for the human population?

A) Earth's ability to absorb by-products of human consumption of fossil fuel energy
B) Availability of water suitable for drinking, irrigation, and other human uses
C) Human willingness to cause the extinction of other species in order to expand the human share of Earth's resources
D) Both a and c
E) All of the above