How would you find out the stereocenters? i think all the oh groups are, but i do not know about the rest.

In this molecule, any carbon atom (a vertex in the diagram) that is connected to 4 unique groups, are stereocenters. This is because if two of those groups were to be switched in terms of positions, you'd get a stereoisomer of the initial molecule. You have to remember that the Hydrogens aren't shown.

For example, the carbon connected to the hydroxy (-OH) group in the bottom right is a stereocenter. It is bonded to 4 unique groups:

-OH

-O-R, with R being the rest of the molecule

-C-R

-H

Hope I helped! xx

the answer would be a