The nebula hypothesis of the formation of the solar system assumes that the material that became the solar system began as a large spherical cloud of gas and dust, rotating slowly. As the solar system formed, most of this material was transformed into a compact, flattened disk, rotating more rapidly. What is the explanation for this change in shape and rate of rotation?

A. the influence of nearby stars
B. differentiation of materials easily vaporized and not easily vaporized
C. alignment with the plane of the Milky Way Galaxy
D. conservation of angular momentum

According to the nebula hypothesis that explains the formation of solar system, there occurs changes in terms of its shape as well as the rate of rotation. It is because of the conservation of angular momentum.

The total angular momentum comprising a system remains same or constant, throughout its period of rotation in the absence of net torque. Due to the increasing density, the nebula eventually collapses, and these clouds of gases collides with one another and forms a large cloud. These clouds attains an average velocity and results in an orderly motion, which eventually take the shape of a disk. This is how with time, the sun and the planets have formed, comprising the solar system.

Thus, the correct answer is option (D).