Some planetesimals in our early Solar System became large enough to attract their neighbors gravitationally and grow by the process called accretion. As they increased in mass they became what astronomers call:

A. particulate planetsB. extrasolar planetsC. protoplanets
D. elliptical planets

Answer is option C (protoplanets).

Explanation:

During the formation of the solar system, a giant cloud of molecular dust collapsed to form stars, which were surrounded by a cloud of gas. The dust and other particles inside the cloud collide and merge together into larger mass through the gravitational and other forces. They continue to grow and become large enough to gravitationally attract other small celestial objects to form protoplanets. Some of the protoplanets continue their growth through the process called accretion and form planets.

Planetesimals - The small celestial objects formed during the early stages of the creation of the solar system.

Protoplanets - The objects formed when planetesimals became large enough to attract their neighboring celestial bodies through the force of gravity and grow by the process known as accretion, where they collide and merge together into larger bodies.

Extrasolar planets - The planets found outside our solar system (orbit another star, not the Sun).