A contour line consists of points that are all at the same elevation, and each line has a different elevation. If two lines crossed, the point where they cross would be a point on both lines, so it would be a point that has two different elevations. That can't exist.
D. hydrogen compounds; hydrogen and helium gas; metal; rock
Explanation:
The solar system theory suggests the formation of the solar system comprised of 98% if the gases as the hydrogen and the helium and least of the metals and rock mass.
