Which sentence has the correct placement of a semicolon?
 a. Because Sarah is absent a great deal; she has a hard time keeping up nevertheless she is willing to
 work overtime.
 b. Because Sarah is absent a great deal, she has a hard time keeping up; nevertheless, she is willing to
 work overtime.
 C.Because Sarah is absent a great deal, she has a hard time keeping up nevertheless; she is willing to
 work overtime.