26. The current carbon dioxide level in the atmosphere is over *
400 ppm (parts per million)
500 ppm
0 550 ppm

The concept of keystone species is controversial among ecologists because most organisms are highly interdependent. if each of the trophic levels is dependant on all others how can we say one is most important

Which set of terms best describes a community of miners who live out in the countryside of west virginia and use specialized geographical equipment to analyze the composition of rocks

What substance acts to prevent sudden ph changes in bodily fluids?