1. The right answer is The nebular hypothesis.
Scientists agree that our solar system results from the contraction, under the effect of its own mass, of a cold and dense interstellar molecular cloud made of gas, hydrogen, and helium essentially, and grains dust covered with ice water. Very quickly, a disc of matter would have formed, turning on itself, slowly on the periphery, quickly in the center. There, at the heart of the disc, the matter being more and more compressed by the movement and the increasing temperature, nuclear fusion reactions would eventually have started. This heart would have started to shine by releasing a phenomenal energy, giving birth to our star, the Sun, 4.56 billion years ago. The rest of the cloud would have continued to gravitate around this very young star, the most volatile compounds being rejected at the periphery under the effect of the very high temperature.
In this primordial nebula, the dust would have progressively agglomerated, forming grains that would have gathered together step by step in boulders, which by aggregating would have gradually given birth to the 9 planets of the solar system, their satellites, and meteorites.
2. The right answer is lines of longitude.
Longitude is a geographical coordinate represented by an angular value, an expression of the east-west position of a point on Earth (or on another sphere). The reference longitude on Earth is the Greenwich meridian.
3. The right answer is topographic map shows elevation.
A topographic map is a reduced-scale map representing the relief determined by altimetry and the human features of a geographical area in a precise and detailed manner on a horizontal plane.
