Tap and needle: what they have in common

1. Step 1. Tap — is part of — Plumbing. Taps.
2. Step 2. Plumbing — works like — Aqueduct. An aqueduct brings water to a city, plumbing distributes it inside; Minoan pipes are older than the Roman aqueducts.
3. Step 3. Aqueduct — uses — Gravity flow. Water flows down a gradient without pumps.
4. Step 4. Gravity flow — is used in — IV drip. The solution flows under gravity.
5. Step 5. IV drip — has part — Syringe. A needle.
6. Step 6. Syringe — has part — Needle. A hollow needle.

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