Which of the Following Best Defines Conformational Isomers

Which of the following best defines conformational isomers?

A) They are the isomers that have the same molecular formula but differ in which atoms are bonded to one another.
B) They are the isomers whose molecules have the same connectivity but whose component atoms have different orientations in space.
C) They are the isomers whose structures are mirror images but cannot be superimposed on one another in any orientation.
D) They are the isomers whose three-dimensional structures differ because of rotation about a σ bond.
E) They are the isomers that differ in the relative positions of substituents in a rigid molecule.