Answer:
The awnser is B
Explanation: no explanation
The given blank can be filled with External.
The stimulus is a physical entity, which can provoke the response in the body of an organism. The hiding of the organism under the rock in response to the predator is and a type of external stimuli, as in this case, the organisms hide themselves inside the rock in response to the predator, which is present outside the body of the organism.
Well, carbohydrates burn and release energy. Nucleic acids give identity (like DNA, RNA). Lipids also give energy, but it's more difficult (they must be first turned into carbohydrates first). Proteins are building blocks for the cells.
Now, knowing all of this should make it easy to choose the correct answer :)
