Inside a car engine, the non-metal element X produces the pollutant oxide Y. Y undergoes a further oxidation in the atmosphere to form Z. During this additional oxidation, $1\ \text{mol}$ of Y combines with $\frac{1}{2}\ \text{mol}$ of gaseous oxygen. What could X be?
- A1, 2 and 3
- B1 and 2 only
- C2 and 3 only
- D1 only