which molecule is an aromatic hydrocarbon?

Brief Explanations:

Aromatic hydrocarbons have a cyclic, planar structure with delocalized $\pi$-electrons following Hückel's rule ($4n + 2$ $\pi$-electrons, where $n$ is an integer). The first structure is an alkene, the second is an alkyne - alkane combination, and the third has a conjugated system but without the cyclic - planar - delocalized structure characteristic of aromatics. Since no correct aromatic hydrocarbon structure is shown among the options, we assume this is a case of none - of - the - above.

Answer:

None of the above options are aromatic hydrocarbons.