D-(-) -Erythrose has the formula HOCH2-CH(OH) -CH(OH)-CHOand the D in its name implies that it can be

Question:

D-(-) -Erythrose has the formula HOCH2-CH(OH) -CH(OH)-CHOand the D in its name implies that it can be degraded to D-(-)-glyceraldehyde. The (-) in its name implies that D-(-)-erythrose is optically active (levorotatory).
When D-(-)-erythrose is reduced (using H2 and a nickel catalyst), it gives an optically inactive product of formula HOCH2-CH(OH) -CH(OH) -CH2OH.
Knowing the absolute configuration of D-(-)-glyceraldehyde (Section 5-14), determine the absolute configuration of D-(-)-erythrose.