Out of the four alternatives, choose the one word that can be substituted for the phrase "a place of shelter for ships". This tests your knowledge of vocabulary related to transport, geography, and maritime locations.

Introduction / Context:
This one-word substitution question focuses on geographical and transport-related vocabulary. The phrase given is "a place of shelter for ships". You must select the word that most accurately describes a sheltered area of water where ships can anchor safely and find protection from rough seas and bad weather.

Given Data / Assumptions:

The subject is ships, so the location is connected with the sea or large bodies of water.
The key phrase is "place of shelter", indicating protection rather than simply a landing place or building.

Some options refer to other kinds of transport (helicopters, planes) or military housing.
The correct word must be commonly used in geography and shipping contexts.

Concept / Approach:
A harbour (also spelled harbor in American English) is a sheltered body of water where ships can anchor safely. It often has natural or artificial barriers that protect vessels from waves and storms. A port is a broader term that usually refers to a town or city with facilities for loading and unloading ships, which may or may not emphasise shelter. A helipad is a landing area for helicopters, a barrack is a building for soldiers, and a runway is used by aircraft in airports. Therefore, harbour is the best match for a place of shelter for ships.

Step-by-Step Solution:
Step 1: Focus on ships and shelter, which clearly places us in the context of maritime geography. Step 2: Recall that a harbour is defined as a sheltered area of water, often next to the coast, where ships are protected. Step 3: Examine option A Harbour and see that it fits the description exactly. Step 4: Consider option C Port. Although many ports are located in harbours, the word port emphasises the town and commercial facilities, not shelter itself. Step 5: Options B Helipad and E Runway refer to aviation and therefore do not relate to ships. Step 6: Option D Barrack refers to soldiers’ accommodation and is clearly unrelated to the sea.

Verification / Alternative check:
Think of real examples: Sydney Harbour, Mumbai Harbour, or Pearl Harbor. These names refer to sheltered water areas where ships can anchor. The associated cities may be called ports because commerce takes place there, but the physical shelter is provided by the harbour itself. For instance, we say Ships took shelter in the harbour during the storm. This sentence would be less natural with port because the emphasis is on safety from weather. This confirms that harbour is the precise term the question is looking for.

Why Other Options Are Wrong:
Option B Helipad is designed for helicopters and may be on land or on a ship, but it is not a water shelter for ships.
Option C Port focuses on a commercial town or facility where ships load and unload goods; some ports may be less sheltered, and shelter is not the defining feature.
Option D Barrack is a military building for soldiers’ accommodation, unrelated to ships or the sea.
Option E Runway is associated with airports and aircraft taking off and landing, not with ships.

Common Pitfalls:
Because harbour and port are closely related, candidates often confuse the two. A helpful distinction is that harbour refers primarily to the sheltered water area, while port refers to the urban and commercial infrastructure associated with shipping. In one-word substitution questions, pay close attention to the exact phrase: here, "place of shelter" clearly points to harbour, not port.

Final Answer:
The one word that best describes "a place of shelter for ships" is harbour.