<human>: Q: When was the tungsten filament introduced?
 A: It was found that very pure tungsten formed filaments that sagged in use, and that a very small "doping" treatment with potassium, silicon, and aluminium oxides at the level of a few hundred parts per million greatly improved the life and durability of the tungsten filaments.
 Does the answer correctly answer the question

OPTIONS:
- yes
- no
<bot>: no