How does the glass of a greenhouse model the carbon dioxide and other gases in EarthÍs atmosphere?

1. The glass absorbs light and releases energy in the form of heat.
   
2. The glass allows light in and traps much of the radiated heat.
   
3. Plants in a greenhouse absorb energy from the sunlight and can grow through the winter.
   
4. The glass blocks incoming light and reduces the amount of heat absorbed by the plants inside. ( 4 or one is my answer but im unsure of it)