The Following Pictures Represent Mixtures of Cis-C₂H₂X₂ Molecules and Trans-C₂H₂X₂

The following pictures represent mixtures of cis-C₂H₂X₂ molecules and trans-C₂H₂X₂ molecules,which interconvert according to the equation cis-C₂H₂X₂ ⇌ trans-C₂H₂X₂.If mixture (1) is at equilibrium,which of the other mixtures are also at equilibrium?

A) mixture (2)
B) mixture (3)
C) mixture (4)
D) None of the other mixtures are at equilibrium.