Crossbow and watt steam engine: what they have in common

1. Step 1. Crossbow — has part — Trigger. A trigger.
2. Step 2. Trigger — is part of — Musket. A trigger.
3. Step 3. Musket — evolved from — Hand cannon. A hand-held gun.
4. Step 4. Hand cannon — evolved into — Cannon. A large hand cannon.
5. Step 5. Cannon — is part of — Ironclad. Artillery.
6. Step 6. Ironclad — has part — Watt steam engine. Steam engines.

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