l and m are two parallel lines intersected by another pair of parallel lines p and q. Show that △ABC ≅ △CDA

In △ABC and △CDA
∠BAC = ∠DCA (Alternate interior angles, as p || q)
AC = CA (Common)
∠BCA = ∠DAC (Alternate interior angles, as l || m)
∴ △ABC ≅ △CDA (By ASA congruence rule)