Examine the Fischer projections of the monosaccharides shown below:

What is their relationship? Are they structural isomers, diastereomers, enantiomers, or epimers? Additionally, classify each as either a D- or L-isomer.

They are structural isomers. They are both L-isomers.

They are diastereomers. Monosaccharide A is a D-isomer, while monosaccharide B is an L-isomer.

They are enantiomers. Monosaccharide A is the D-isomer, while monosaccharide B is the L-isomer.

They are epimers and they are both D-isomers.