A 40 W bulb is left on from 9:00 p.m. to 6:30 a.m.

From 9:00 p.m. to 6:30 a.m. is 9.5 hours. Convert the bulb’s power to kilowatts: 40 W = 0.040 kW. Energy used is power × time, so 0.040 × 9.5 = 0.38 kWh; the correct choice is 0.38 kWh.

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