Titanium and steam locomotive: what they have in common

1. Step 1. Titanium — is material for — Mars rover. The wheels and parts are aluminium and titanium.
2. Step 2. Mars rover — evolved from — Lunokhod. Planetary rovers.
3. Step 3. Lunokhod — has part — Wheel. Wheels.
4. Step 4. Wheel — is part of — Steam locomotive. The steam engine turns the driving wheels.

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