Which of the following represents a hydrocarbon that contains one double bond somewhere in the carbon chain?
alkane
alkene
alkyne
substituted hydrocarbon

i know it's not c, alkyne

The answer is alkene.

An alkane is a saturated hydrocarbon, thi is it has only single bonds.

Alkenes and alkynes are unsaturated: alkenes have double bonds and alkynes have triple bonds.

Subsituted hydrocarbon, is a hydrocarbon with one hydrogen substituted by another element or a group.

For example:

CH3 - CH - CH3
           |
          F

Ais the correct answer