A glass chimney stops an oil lamp from smoking because it improves the supply of oxygen and helps heat the flame for complete combustion. When an oil lamp burns without enough oxygen, it produces smoke due to incomplete burning of the oil. The glass chimney creates a steady airflow by convection, allowing more oxygen to reach the flame.

This increased oxygen helps the flame burn hotter and cleaner. Additionally, the heat trapped inside the chimney ensures the oil burns fully, reducing the smoke. Both effects work together to keep the flame bright and smoke-free.

Here’s why the other options are less complete:
- Increasing oxygen alone helps but does not fully prevent smoke without proper heat.
- Heat alone is not enough if oxygen supply is limited.
- Saying "neither" is incorrect because both factors contribute.

In simple terms, the glass chimney ensures a good flow of air and heat to maintain clean combustion. This is why oil lamps with chimneys burn longer and more efficiently, producing less smoke and soot.

Understanding this helps us appreciate basic principles of combustion and how simple designs improve everyday tools.