Underground water tunnel and turbine: what they have in common

1. Step 1. Underground water tunnel — is part of — Qanat. A gently sloping tunnel through which water flows to the fields.
2. Step 2. Qanat — uses — Gravity flow. Water flows by gravity.
3. Step 3. Gravity flow — is used in — Water wheel. Falling or flowing water turns the wheel.
4. Step 4. Water wheel — evolved into — Turbine. The water turbine evolved from the water wheel.

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