Which of the following terms correctly describe(s) the structural relationship between cis-1,3-dimethylcyclopentane and trans-1,3-dimethylcyclopentane?

A) enantiomers
B) diastereomers
C) geometric isomers
D) both A and C
E) both B and C

Cis-1,3-dimethylcyclopentane and trans-1,3-dimethylcyclopentane are diastereomers because they are stereoisomers that are not mirror images of each other. They are also geometric isomers, a term specifically used to describe compounds that differ in the spatial arrangement of groups around a double bond or a ring system, like in this case.