Final answer:
The correct order of priority when arriving at a navigation lock is military craft, commercial vessels, fishing vessels, then pleasure craft.
Step-by-step explanation:
When arriving at a navigation lock, the order of priority is generally as follows: military craft, commercial vessels, fishing vessels, then pleasure craft.
So the correct answer is d. Military craft, commercial vessels, fishing vessels then pleasure craft. This hierarchy ensures that vessels that serve critical functions or larger-scale economic activities have priority access to passage through the lock. Pleasure craft are usually given the lowest priority because they are often smaller and used for personal enjoyment rather than critical services.