Amolecule of an unsaturated hydrocarbon must have 1) at least one single carbon-carbon bond 2) at least one multiple carbon-carbon bond 3) two or more single carbon-carbon bonds 4) two or more multiple carbon-carbon bonds

2) at least one multiple carbon-carbon bond.

Explanation:

So, A molecule of an unsaturated hydrocarbon must have 2) at least one multiple carbon-carbon bond.

indicate valleys, hills, steepness and gentleness of slopes.

explanation:

contour lines on a map indicate elevation, or depth. numeric notations on contour lines refer to the level of elevation, or height about sea level.