What is the relationship between 2,2-dimethyl[2.2.2.0]tricyclooctane and 3,3-dimethyl[2.2.2.0]tricyclooctane?
A. they are constitutional isomers
B. they are stereoisomers
C. 2,2-dimethyl[2.2.2.0]tricyclooctane is not a valid name
D. 3,3-dimethyl[2.2.2.0]tricyclooctane is not a valid name
E. neither given name is valid