Final answer:
The port docking fee is a fixed cost for a party cruise ship because it is a set charge that does not vary with the number of passengers or the level of consumption onboard. So the correct answer is option b.
Step-by-step explanation:
Among the options provided for a party cruise ship's expenses, the port docking fee would be considered a fixed cost. Fixed costs are consistent expenditures not affected by the level of production or the amount of services provided.
The port docking fee is a set charge that must be paid regardless of the number of passengers on the ship or the amount of food and drink they consume. Therefore, it remains constant and is a fixed cost to the cruise operation.
On the other hand, expenses such as food served (a), cocktails that are served (c), and dishwashing detergent (d) are variable costs. These costs fluctuate with the number of passengers on board and the amount of consumption of these items. The more passengers there are, or the more they consume, the higher these costs will be.