The correct answer is A. a rotating cloud of dust and gas.
Explanation:
Nebulae are regions of the interstellar medium (clouds) made up of gases (mainly hydrogen and helium) and dust. In other words, nebulae are concentrations of gas in which we find hydrogen, helium and stardust in greater quantities. They are structures that are actually very important for the universe, this because inside it is the place where stars are born, which arise due to the condensation and aggregation of matter. The nebular theory states that the Solar System reached the form current from a solar nebula (a gas cloud), more than 4.5 billion years ago. The large cloud of molecular gas was affected by a certain phenomenon that would have taken place in the vicinity. Like the explosion of a supernova or the passage of a star that would produce a strong gravitational impact. The result of this event made the matter agglomerate in different places. The high concentration of matter caused the nebula to collapse. Becoming a protostar, (bodies whose characteristic is to be surrounded by clouds and contain preplanetary matter inside), that is, gaseous matter in the outermost part and solid inward. At the core of this structure, the temperature is so dominant that nuclear reactions take place to compensate for the gravitational force. This leads to a hydrostatic equilibrium and the formation of a fundamental star: the Sun. The rest of the mass flattened, forming a protoplanetary disk where the protoplanets were being formed, which would evolve to become the current planets, their satellites and the others bodies of the solar system.
Kepler's third law relates the semi-major axis of the orbit to its sidereal period. The major axis is the total length of the long axis of the elliptical orbit (from perihelion to aphelion).
I would say true. I say this because there have been times where scientists find out that there are better ways of performing experiments, or found that certain materials work better for certain tasks. (Especially true in medicinal fields!)
