Answer:
The salary paid to the new member ( B)
Explanation:
The marginal cost is the cost incurred by a business or organization for the production or addition of one additional unit of good or service to the already existing number and this additional unit cause a change in opportunity cost as well.
The addition of an employee to the event management crew will result to a marginal cost in the form of salary been paid to the new member/employee
hence option B is the correct. option D would have be correct option if the question requested the total Marginal cost incurred by the event management crew