Mom rushes to the store and gets some milk. Is this a compound sentence, complex sentence or a simple sentence

Thermal energy is not in the process of being transferred ; it is not in transmit, but it remains in part of the internal energy system. Heat is Energy is in the process of being transferred from a hotter system.

Examples of thermal energy:

-The warmth from the sun.

-A cup of hot chocolate*

-Baking in an oven.

-The heat from a heater.

I hope this Helps!