Which one(s) contribute the most to the mass of a plant?

The correct answer is D II and III only.

Explanation: The mass of a plant primarily comes from two sources: carbon dioxide absorbed from the air (which contributes significantly to biomass through photosynthesis) and water taken up from the soil. While soil may provide nutrients, it does not significantly add to the mass of the plant itself. Hence, both carbon (from CO2) and water are the main contributors to a plant’s mass.