Answer:
B) Increase substrate concentration.
Step-by-step explanation:
As the organism is living in environment with high temprature and (acidic) low pH the enzymes are affected as follows :
Increased Temprature : Initially the rate of reaction increase (10 degrees rise in T causes 50 to 100% rise in activity of enzyme) but ultimately over the period of time enzymes become denatured , hence they cannot stimulate the rate of reaction even if the substrates are added.
Effect of pH: pH is the factor of stability of the enzymes but if the pH becomes extremely low or high the activity of enzymes is affected in such a way resulting in complete loss of activity of enzyme hence addtion of substrates can't increase the activity.
Thus among the given options , option B is the right choice as the increase in the substrate won't increase the activity of the enzyme as they are already denatured.