Which body systems are involved in the maintenance of homeostasis? All organ systems
Nervous and circulatory systems
Nervous and respiratory systems
Nervous, circulatory, respiratory and excretory systems.

1. b

2. c

3. a

Explanation: A chemical reaction in equilibrium is actually in a dynamic euqilibrium, which means that changing a condition will make the equilibrium move to counteract the action and reestate the equilibrium.

For example, in the reaction:

N2(g) + 3H2(g) ⇄ 2NH3(g)

1. Adding H2: if you add the reagent, to reestate the equilibrium, the reaction will produce more products so, it will move to the right;

2. A catalyst doesn't interfere in the equilibrium, because it moves to the right and to the left at the same extent. Therefore, there is no effect.

3. Decrease the pressure: when you decrease the pressure of a reaction, the equilibrium will make the pressure increase again by moving towards the side of the reaction which has more molecules, so, it shifts to the left;