This answer is not correct. The best way to answer this question is to draw the 3d view into a Fischer projection. When you do this, it should look like the following projection. Note that there is only one chiral carbon atom that is different than the Fischer projection shown in the problem. When stereoisomers with more than one chiral center differ at only one chiral carbon atom, they are related as epimers...a specific sub category of diastereomers.