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.
I am pretty sure the answer is a
The correct answer is buildup of toxins.
One of the essential action of the liver is to process various kinds of toxins and to eliminate it out of the system of the organism. Although it is known as a toxin processor, it is not resistant to the toxins itself. As the liver is the main site for drug decontamination and stimulation, thus, the improper functioning of the liver may lead to the accumulation of toxins.
Mutualism, they both help each other out and both benefit
