Which of the following describes a single population?
A. A group of bacteria all of the species Bacillus subtilis
B. All insects occupying three hectares of farmland
C. An exact count of 315 animals in a fenced plot of land
D. All the birds counted in one day by census takers in the United States
E. All the animals and plants on an isolated island
Answer: A. A group of bacteria all of the species Bacillus subtilis