The list below shows some changes that may take place in a lake polluted with nitrogen-containing fertiliser. In what order do these changes happen?
- A1 $\rightarrow$ 2 $\rightarrow$ 3 $\rightarrow$ 4
- B2 $\rightarrow$ 1 $\rightarrow$ 4 $\rightarrow$ 3
- C3 $\rightarrow$ 4 $\rightarrow$ 2 $\rightarrow$ 1
- D4 $\rightarrow$ 3 $\rightarrow$ 1 $\rightarrow$ 2