Q.32 D, L series of the saccharides

About the configuration of trihydroxyglutaric acid HOOCCH(OH)CH(OH)CH(OH)COOH, 1) How many configurations occur about the two asymmetric carbon atoms C-2 and C-4? 2) In which case is C-3 asymmetric carbon atom in? How many isomers does trihydroxyglutaric acid have when the above is taken into consideration?