Correct option is D
Plants absorb phosphorus mainly as dihydrogen phosphate (H₂PO₄⁻) and hydrogen phosphate (HPO₄²⁻) ions, depending on soil pH.
• At acidic pH: H₂PO₄⁻ dominates
• At alkaline pH: HPO₄²⁻ is more available
Therefore, both forms are important sources of phosphorus.