Pumped-storage station and petri dish: what they have in common

1. Step 1. Pumped-storage station — is made of — Concrete. The reservoirs and dam are concrete.
2. Step 2. Concrete — is material for — Sewage treatment plant. The tanks are concrete.
3. Step 3. Sewage treatment plant — uses — Culture medium (agar). Waste water is cleaned by activated sludge — bacteria.
4. Step 4. Culture medium (agar) — uses — Petri dish. Agar in dishes.

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