Rubble stone mound and freezer: what they have in common

1. Step 1. Rubble stone mound — is part of — Breakwater. A stone ball.
2. Step 2. Breakwater — is made of — Concrete. Concrete blocks.
3. Step 3. Concrete — is material for — Sewage treatment plant. The tanks are concrete.
4. Step 4. Sewage treatment plant — has part — Compressor. Blowers supply oxygen to the microbes.
5. Step 5. Compressor — is part of — Freezer. A compressor compresses the refrigerant.

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