What Was a Central Component of the Improvements in Sanitation

What was a central component of the improvements in sanitation in the nineteenth century?

A) Horses carried many of the diseases that afflicted humans.
B) Communal baths would reduce the spread of dangerous bacteria.
C) Excrement from outhouses could be carried off by water through sewers at low cost.
D) Most diseases were carried into cities by rural laborers who came into the cities for work.