How Did the Temperature of the Solar Nebula Develop

Multiple Choice

How did the temperature of the solar nebula develop?

A) The nebula formed from cold gas and dust, and it remained cold until sufficient oxygen had accumulated so that combustion was possible.
B) The nebula formed from cold gas and dust, and it remained cold until nuclear reactions developed.
C) The gas and dust remained cold as they collapsed to form a much denser nebula. Here friction developed between the particles, and this gradually raised the temperature.
D) As the nebula collapsed, gravitational potential energy was converted into kinetic energy, and the temperature rose.