If Carpentry Positions a and B Required Identical Skill Levels

If carpentry positions A and B required identical skill levels, other things constant, which one of the following would most likely elevate the wage rate of position A relative to position B?

A) The work place of position A is in the intense heat of the sun, whereas the work place of B is air-conditioned.
B) Position A is a safe office job; position B requires the employee to operate a dangerous saw.
C) Position A offers steady employment, whereas employees holding position B are often laid off.
D) Position A offers more sick leave and more paid holidays.