Gallium arsenide and stone tool: what they have in common

1. Step 1. Gallium arsenide — is material for — LED. The first LEDs were gallium arsenide phosphide.
2. Step 2. LED — is part of — Billboard. LED screens.
3. Step 3. Billboard — is made of — Paper. The poster is paper.
4. Step 4. Paper — is material for — Fire lance. The barrel of a fire lance is a paper or bamboo tube.
5. Step 5. Fire lance — evolved from — Spear. The fire lance was a spear with a tube of gunpowder — the first step to firearms.
6. Step 6. Spear — has part — Stone tool. Early spearheads were made of stone.

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