Harbour engineering terminology: identify the correct statements regarding moles, quay walls, and types of breakwaters.

Introduction / Context:
Ports and harbours use a family of specialized structures. Knowing the correct names and roles—moles, quay walls, and breakwaters—helps in reading plans and specifying works.

Given Data / Assumptions:

• A mole is a breakwater or similar structure that also accommodates operations on its crest.
• A quay wall is a retaining wall forming a berth edge for cargo handling.
• Breakwaters are commonly categorized (e.g., rubble mound, composite, and vertical/upright types).

Concept / Approach:
Moles differ from purely protective breakwaters in that they provide working platforms. Quay walls retain fill and provide berthing faces. Breakwaters are grouped by cross-section and construction type, commonly into three broad classes.

Step-by-Step Solution:
Confirm (a): Mole = protective structure usable as a working platform.Confirm (b): Quay wall = retaining/berthing wall used for loading/unloading.Confirm (c): Broadly three classes are recognized.Therefore, all statements are correct.

Verification / Alternative check:
Harbour engineering texts describe these standard definitions.

Why Other Options Are Wrong:

• Choosing a subset would omit accepted terminology and classification.

Common Pitfalls:

• Misspelling 'quay' as 'guay'; the accepted spelling is 'quay'.

Final Answer:
All of the above.