Bit and bridle and electric motor: what they have in common

1. Step 1. Bit and bridle — has part — Headband. Straps on the head.
2. Step 2. Headband — is part of — Headphones. A band that presses the cups.
3. Step 3. Headphones — is part of — Walkman. Headphones.
4. Step 4. Walkman — has part — Electric motor. A motor.

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