A farmer is aware that his soil requires phosphorus and potassium. He can choose from four fertilisers: 1 $\text{NH}_4\text{NO}_3$; 2 $(\text{NH}_4)_3\text{PO}_4$; 3 $\text{KNO}_3$; 4 $(\text{NH}_2)_2\text{CO}$. Which fertilisers ought he to use?
- A1 and 2
- B1 and 4
- C2 and 3
- D3 and 4