Silo and freezer: what they have in common

1. Step 1. Silo — is made of — Concrete. Later — concrete.
2. Step 2. Concrete — is material for — Sewage treatment plant. The tanks are concrete.
3. Step 3. Sewage treatment plant — has part — Compressor. Blowers supply oxygen to the microbes.
4. Step 4. Compressor — is part of — Freezer. A compressor compresses the refrigerant.

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