The third alternative is correct (C).
When two sentences are connected because they are complementary, an element is needed to contain them, that is, a conjuction. In that case, it could have been "and". However, who wrote used the comma to amend the periods, in a wrong way because it affected the cohesion of the stretch.
"The local classic car auction raised $ 12,000 for local charities and the mayor is designating the funds to the children's hospital."
