TOEFL Listening: ETS-TOEFL听力机经 - E9EZP16O4MFKJE83P$

What points does the professor make about the lightbulbs used in the first generation of skyscrapers? A. The lightbulbs did not require much energy. B. The lightbulbs did not produce much light. C. The use of multiple lightbulbs could significantly affect a room's temperature. D. The use of multiple lightbulbs increased the cost of operating skyscrapers.