how is there no centre of symmetry in this case? the question was whether the following compounds have the center of symmetry or not .the question was :


And the answer is that there is no center of symmetry .how? according to me, there should be the centre of symmetry. I have made it like this:

on asking my teacher how there is no center of symmetry he told me that since it is a Fischer projection, therefore, the horizontal lines are above the planes. therefore there will be no center of symmetry. I understand that if the horizontal lines are out of the plane then there will be no COS. but what I don't understand how come the horizontal lines are above the plane/out of the plane. please explain.
One way to quickly get a visualization without building a 3D model (having a model is more instructive, though):


Go to https://chemapps.stolaf.edu/jmol/jsmol/simple.htm
Click on Load by name and type "(2S,3S)-Butane-2,3-diol"
Click on console and type "rotate branch @2 @4 180" to get a conformation that is easy to compare with the Fisher projection.