Solar water heater and mechanical clock: what they have in common

1. Step 1. Solar water heater — has part — Window glass. The glass on top creates a greenhouse effect.
2. Step 2. Window glass — is part of — Gothic cathedral. Stained glass.
3. Step 3. Gothic cathedral — has part — Tower clock. A tower clock.
4. Step 4. Tower clock — is a kind of — Mechanical clock. A clock.

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