Oil refining and chisel: what they have in common

1. Step 1. Oil refining — uses — Fractional distillation. Rectification columns.
2. Step 2. Fractional distillation — is used in — Chemical plant. Separation.
3. Step 3. Chemical plant — is made of — Brick. The furnaces and towers are brick.
4. Step 4. Brick — is material for — Metro. The vaults of the first tunnels are brick.
5. Step 5. Metro — uses — Tunnel. Tunnels.
6. Step 6. Tunnel — uses — Chisel. Hezekiah’s Tunnel was cut by hand with chisels.

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