The fuel tank of an airplane has a device that measures the fuel’s temperature. Before the airplane took off, the temperature of the fuel was 27°C. After the airplane had been flying for one hour, the temperature of the fuel had decreased to 3°C. Which of the following must have happened to the molecules of the fuel?


A. The molecules got farther apart.

B. The fuel gained cold molecules.

C. The molecules started moving slower.

D. The molecules became smaller in size.