The diagram illustrates a flow chart for producing fertiliser. In the flow chart, what do W, X, Y and Z represent?
- A$W = \text{H}_2$, $X = \text{N}_2$, $Y = \text{high}$, $Z = \text{NH}_3$
- B$W = \text{O}_2$, $X = \text{SO}_2$, $Y = \text{high}$, $Z = \text{SO}_3$
- C$W = \text{O}_2$, $X = \text{SO}_2$, $Y = \text{low}$, $Z = \text{SO}_3$
- D$W = \text{N}_2$, $X = \text{H}_2$, $Y = \text{high}$, $Z = \text{NH}_3$