Task: Question Answering
Input (English): Background Paragraph: A vapor light produces visible light by electroluminescence. The bulb contains a small amount of solid sodium or mercury as well as a mixture of neon and argon gases. When an electric current passes through the gases, it causes the solid sodium or mercury to change to a gas and emit visible light. Sodium vapor lights, like these streetlights, produce yellowish light. Mercury vapor lights produce bluish light. Vapor lights are very bright and energy efficient. The bulbs are also long lasting. 
Story: James is driving down the street in his town. For some reason today hes very curious about the things that he sees. He looks around as hes driving and the street lights catch his attention. He realizes that he's never seen someone changing the bulbs in a street light. He also wonders if its a film on the light that makes them have that color or something inside. 
Question: Given James sees the yellow street light light up, which type of vapor light is it likely to be, Mercury or Sodium?
Output (English): Sodium.