For the Pair of Compounds, Select a Correct Characterization from the Response

For the pair of compounds, select a correct characterization from the response list: pentane and 2, 2-Dimethylpropane.

A) are constitutional isomers
B) have the same number of carbon atoms but are not constitutional isomers
C) both exist in cis-trans forms
D) one but not the other exists in cis-trans forms