D-Alanine and L-Alanine are technically known as

ANS:B - enantiomers

Diastereomers are compounds that have similar configuration at some carbon and dissimilar configuration at some carbons.

Whereas epimers are compounds that differ in configuration at only one chiral carbon.

The point of difference arises in the fact that epimers have only one chiral carbon which is different in configuration whereas diastereomers can have any number of different configuration around its chiral carbons (except all being different).

If two compounds would differ at all stereocentres, they would be enantiomers or if a pair of stereoisomers are non-superimposable mirror images of each other, then they are enantiomers.