Assuming a chair conformation, which of the following configurations will always have both methyl groups in equatorial positions at the lowest energy conformation?
cis-1,2-dimethylcyclohexane
cis-1,3-dimethylcyclohexane
trans-1,3-dimethylcyclohexane
trans-1,2-dimethylcyclohexane
cis-1,4-dimethylcyclohexane
trans-1,4-dimethylcyclohexane