The advantages of automation include: (I) reduced output variability. (II) reduced variable costs. (III) machines don't strike or file grievances. (IV) machines are always less expensive than human labor.

(III) machines don't strike or file grievances.

(IV) machines are always less expensive than human labor.

Explanation:

The advantage of automation among the option is:

(III) machines don't strike or file grievances - Machine has the advantage of not going on strike or filing grievances. It just obey instruction. Strike are human way of showing grievances. With automation, there is no issue of strike or filing for grievance.

(IV) machines are always less expensive than human labor - Machines as a means of automation are very cheap when compared to human labor. The only added cost for machine is the added cost after the cost of purchase. For human labor, the cost is not fixed or predictable.