During cultivation of microorganisms in a fermenter, various parameters are controlled by appropriate sensor (probe). Match each probe in Group I with the appropriate response mechanism in Group II.

Group I (Probe)	Group II (Response)
P. Thermistor	1. Activation of acid/alkali pump
Q. Oxygen electrode	2. Activation of vegetable oil pump
R. Metal rod	3. Activation of hot/cold water pump
S. pH electrode	4. Increase/decrease in stirrer motor speed

A. P-2, Q-3, R-1, S-4

B. P-1, Q-2, R-4, S-3

C. P-3, Q-2, R-4, S-1

D. P-3, Q-4, R-2, S-1

Answer: Option D