This is a tutorial question I need to do, I initially thought the question was testing whether students properly understand (1) chair conformations of decalin, and (2) that the leaving group and the breaking bond should be 'anti-periplanar'.
However, the third molecule also turned out to have undergone the elimination reaction when the first didn't, so I am very confounded. I have drawn all possible conformations of cis-Decalins, but no single conformation seems to allow $\ce{C-OTs}$ bond and $\ce{C-OH}$ bond to be anti-periplanar. Am I missing out something?