What is the ozone layer?
A. thin layer in the lower atmosphere that protects Earth from ultraviolet rays
B. thin layer in the upper atmosphere that protects Earth from ultraviolet rays
C. thin layer in the upper atmosphere that protects Earth from supersonic rays
D. thin layer in the lower atmosphere that protects Earth from supersonic rays
What do all ecosystems have ?
A. biotic p21 only
B. abiotic p21 only
C. producers only
D. biotic and abiotic p21