Which revision corrects the comma use in this sentence?
"I intend to write an editorial on one of these subjects: employers should be liable for the life and health of employees; the boycott is a legitimate method of obtaining employees' demands; and national expositions do not benefit the cities, in which they are held."
a) I intend to write an editorial on one of these subjects, employers should be liable for the life and health of employees; the boycott is a legitimate method of obtaining employees' demands; or national expositions do not benefit the cities, in which they are held.
b) I intend to write an editorial on one of these subjects: employers should be liable for the life and health of employees, the boycott is a legitimate method of obtaining employees' demands or national expositions do not benefit the cities, in which they are held.
c) No correction is necessary.
d) I intend to write an editorial on one of these subjects: employers should be liable for the life and health of employees, the boycott is a legitimate method of obtaining employees' demands, or national expositions do not benefit the cities in which they are held.