Option 1 suggests that volcanic action and photosynthesis add carbon dioxide to the carbon cycle. This is partly true as volcanic action does release CO2. However, photosynthesis absorbs CO2 and thus does not `add` it to the carbon cycle.

Option 2 posits that respiration is the only source of CO2 in the carbon cycle. While it is correct that organisms release CO2 through respiration, it`s not the only source.

Option 3 is the correct answer. Volcanic action, respiration and decay of organic matter all release CO2 into the atmosphere. Volcanoes release CO2 trapped in the earth`s mantle, organisms release CO2 through respiration and as organic matter decays, it also releases CO2.

Option 4 incorrectly includes photosynthesis as a process that adds carbon dioxide to the carbon cycle. It should be noted that photosynthesis is a process taken by plants and algae to convert CO2 and sunlight into oxygen and glucose, thus reducing the amount of CO2 in the atmosphere.