Large amounts of human insulin may be made using modified $E.\ coli$ bacteria. Four stages in this production method are given below. In which order do these stages occur?
- A$1 \rightarrow 2 \rightarrow 3 \rightarrow 4$
- B$1 \rightarrow 3 \rightarrow 4 \rightarrow 2$
- C$2 \rightarrow 3 \rightarrow 4 \rightarrow 1$
- D$4 \rightarrow 1 \rightarrow 2 \rightarrow 3$