Most of the control mechanisms that maintain an internal steady state are based on in which a change in a variable triggers mechanisms that reverse that change.

The correct answer will be- negative feedback

Explanation:

The internal environment of the animals is maintained through a process known as the Homeostasis which is controlled by the feedback loops.

The feedback represents a situation in which the response of the loop impacts or influences the stimulus or the input.

The loop in which the change in a variable trigger the reversal of the mechanism is known as the negative feedback which reverses the change to opposite direction like the increase in the concentration of one substance cause the decrease of another substance.

Thus, negative feedback is the correct answer.

answer: - b cells

explanation: -

so, the b cells mediate their action by identifying the antigens present on the surface of the pathogens and then producing antibodies in return to mediate its effect.

i think that c)gold was found there

but i am not sure