You will be given a definition of a task first, then some input of the task.
In this task, you are given a context and four options. Each option is a suggested ending for the context. You should read the context and pick the best ending for the context. Please answer with "A", "B", "C", and "D".

[header] How to study the phenomenon of light as a nonequilbirum state of matter [title] Understand how thermodynamic systems are categorized. [step] Thermodynamic systems in nature are divided into two types. One is systems that are at equilibrium state with the environment and the other is systems that are in a state of nonequilibrium with the surroundings. <sep> (A) On earth, nature has a preference for systems that are at an equilibrium state with the surrounding. This is so due to the principle of minimum energy that every object in the universe aspires to have. (B) For example, gas rising in temperature throughout the day can be divided into microorganisms in the environment. [substeps] For example, gas rising in temperature in the atmosphere can be divided into molecules in the environment. (C) [substeps] Equilibrium is fundamental in thermodynamics. Other systems include stars, planets, and oceans. (D) [title] Learn about the term " rock hydrodynamics ". [step] Rock hydrodynamics refers to the transfer of water to the earth's surface.
Output:
A