People may find it unbelievable that two hundred years ago people did not link illness     1     environmental problems. In London, drinking polluted water led     2     many deaths from cholera. It always started in the poor neighborhood, and then it spread to the richer areas as the servants infected     3     the illness passed it on. Many doctors suspected    4    polluted water was     5     (blame). John Snow’s     6     (finding) proved that the dirtier the water, the     7     (severe) the illness. Therefore, they concluded that water must be     8     (pure). They instructed the     9     (handle) be removed from pumps if the water carried the virus. Thanks     10    John Snow, cholera was defeated eventually.