Final answer:
The correct answer is A) Planetary accretion; gravitational attraction. Planetary accretion is the process by which planets form through gravitational attraction and clumping of materials in a spinning disk around a young star.
Step-by-step explanation:
The planets in the solar system are believed to have formed as a result of a process known as planetary accretion, which is caused by gravitational attraction. The option that correctly fills in the blanks would be A) Planetary accretion; gravitational attraction.
During the solar system's formation, a solar nebula, consisting of gas and dust, collapsed due to gravitational forces, leading to the creation of a spinning disk around our nascent Sun. Small bodies, or planetesimals, formed within this disk, which gradually grew through the process of accretion, where they attracted more material and combined to form larger bodies. Over time, with further accretion and heating, these bodies differentiated and evolved into the various planets we observe today. In the outer solar system, the presence of ices and rocks allowed for the formation of giant protoplanets that captured hydrogen and helium gas and became the giant planets.