A coral reef is a complex system. In a complex system, many variables may be changing at the same time. What would be most helpful in trying to understand the overall system of a coral reef?

A. A picture that shows an unusual event in a coral reef system.
B. Data that shows the temperature of the water in the coral reef system.
C. Data that shows the number of anemones in a coral reef system.
D. A picture that shows a typical example of coral reef system.