Decreasing variable resistance increases series current and voltage across fixed resistor

Steps:

• Total circuit resistance decreases as variable resistor value is reduced.
• Battery voltage is constant, so current increases per Ohm's law (I = V / R_total).
• Ammeter measures total current, which rises.
• Voltmeter measures voltage across fixed resistor (V = I * R_fixed), which increases with current.

Why D is correct:

• Ohm's law states voltage across a resistor equals current times resistance; with fixed R and rising I, V rises.

Why the others are wrong:

• A: Current increases, not decreases, due to lower total resistance.
• B: Matches D but listed separately; assumes duplication, but current and voltage both increase.
• C: Voltage across fixed resistor increases with current, not decreases.

Final answer: D