Which of the following is an example of an open system?

A. a sealed aquarium containing plants and animals
B. The earth
C. The ocean
D. a closed thermos

The answer is C because all of the spheres of the earth exchange energy and mass.

That is true tge cactus as a structural adaptation to its envirinment has it leaves reduced to spines. but this doesnt mean it cant produce food it produces food because of the presence of chlorophyll in its stem