Which of the following was not a major cause of a largescale loss of life in late medieval western europe ?

a: famine
b: the crusades
c: the hundred years’ war
d: the bacterium yesenia pestis

Ifound the exercise on the internet. attached is the list mentioned above.in order for a compound to be considered optically active it can't have any axis or plan of symmetry. the molecule  shouldn't also  be superimposable on its mirror image.with such considerations, the compounds that are optically active are: -third compound on the first image is optically active; -second and third compound from the second image are optically actives.