Minimize total resistance to maximize current and voltage across fixed resistor

Steps:

• Identify components: thermistor (NTC, resistance decreases with heat) and photoresistor (LDR, resistance decreases with light).
• Assume series circuit with fixed resistor for shared current.
• Voltage across fixed resistor = I × R_fixed; maximize I by minimizing total resistance.
• Total R minimized when both variable resistances are lowest: warm for thermistor, bright for LDR.

Why D is correct:

• Warm and bright lowers both resistances (NTC and LDR), minimizing total R, maximizing I and thus V_fixed per Ohm's law.

Why the others are wrong:

• A: Cold raises thermistor R; dark raises LDR R; total R maximized, I and V_fixed minimized.
• B: Cold raises thermistor R despite bright lowering LDR R; total R still high, V_fixed not maximal.
• C: Dark raises LDR R despite warm lowering thermistor R; total R still high, V_fixed not maximal.

Final answer: D