Escalator and cannon: what they have in common

1. Step 1. Escalator — has part — Roller chain. A chain pulls the steps.
2. Step 2. Roller chain — works like — Continuous track. A track is a closed chain of hinged links driven by a sprocket; the principle is that of a roller chain, on a different scale.
3. Step 3. Continuous track — is part of — Infantry fighting vehicle. Tracks.
4. Step 4. Infantry fighting vehicle — has part — Cannon. An autocannon.

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