Tunnel and radar: what they have in common

1. Step 1. Tunnel — uses — Dynamite. Drilling and blasting.
2. Step 2. Dynamite — evolved from — Gunpowder. A replacement for gunpowder in mining.
3. Step 3. Gunpowder — is used in — Anti-aircraft gun. Gunpowder propels the projectile.
4. Step 4. Anti-aircraft gun — uses — Radar. Radar guidance.

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