Q. Aonsider the following :1. Photosynthesis      2. Respiration       3. Decay of organic matter     4. Volcanic action  Which of the above add carbon dioxide to the carbon cycle on Earth ? 

1. 1 and 4 only
2. 2 and 3 only
3. 2,3 and 4 only
4. 1,2,3 and 4