Howitzer and monitor: what they have in common

1. Step 1. Howitzer — uses — Gunpowder. Gunpowder propels the projectile.
2. Step 2. Gunpowder — is used in — Landmine. Chinese mines of the 13th century were filled with gunpowder.
3. Step 3. Landmine — is used in — Minesweeper. Against sea mines.
4. Step 4. Minesweeper — has part — Sonar. Searching for mines.
5. Step 5. Sonar — works like — Ultrasound scanner. A medical sonar: the same echo principle.
6. Step 6. Ultrasound scanner — has part — Monitor. A screen.

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