If $(\mathrm{AB}) // (\mathrm{CD}), (\mathrm{AB}) \perp (\mathrm{EF})$ and finally $(\mathrm{EF}) \perp (\mathrm{GH})$.

What can be said about $(\mathrm{CD})$ and $(\mathrm{GH})$?
(EF) $\perp$(GH) and (EF) $\perp$(AB)

Therefore (GH) // (AB)

Or (AB) // (CD)

Therefore (CD) // (GH)

Some of these reasonings are more computational, in these cases, we use arrows: