How many stereoisomers can exist for 4,5-bis(3-hydroxyoct-1-en-1-yl)cyclopentane-1,3-diol?
The question is tricky, because


the two ends of the wavy bond are both stereogenic units (chiral cyclopentane ring carbon atom, and the double bond), so there is some additional unintentional ambuguity, but it's not a big deal, because the legend at right explains the situation somewhat;
it in fact asks “How many … stereoisomers does this structure represent?” (because of some stereogenic units with unspecified configuration) instead of “how many … stereoisomers does it have?”.


The unspecified-configuration stereogenic units are two chiral carbons and one double bond, which give total 8 stereoisomers.



The first one (top left) has a plane of symmetry, the other 7 stereoisomers are optically active.