The correct answer is C) Labor.
Niall is increasing labor resource.
Labor can be understood as the human action that generates a result to produce something of value. In this case, Niall has expanded his science-fiction webzine, hiring four new articles editors, a copy editor and a has replaced his webmaster. What Niall has done is to increase the labor resource because when expanding, he needs to invest more in human resources to update his business, to be more efficient and productive in order to generate more income.
