Joel has a terrarium. The terrarium is a sealed container with both plants and animals. Inside the container, the plants and animals grow and reproduce. From time to time, Joel places the terrarium on a balance and always gets the same reading, 1525.3 grams. This is evidence that best supports which of the following laws of living systems?

A. A Law of thermodynamics
B. B Law of conservation of energy
C. C Law of motion
D. D Law of conservation of mass