Which of the following statements is supported by the nebular hypothesis regarding the formation of our solar system?

A  The Sun became a star when its temperature and density became so great that nuclear fusion began.

B  The moon is believed to have been a protoplanet that passed close to Earth and was captured by its gravitational field.

C  The initial atmospheres of Earth and other planets close to the Sun were rich in ammonia and carbon dioxide.

D  The solar system was formed by the expansion of a relatively small cloud of gas and space dust.

E  The Sun and the rest of the solar system were formed approximately one billion years ago.