A setup for determining the percentage of oxygen in $150\,\text{cm}^3$ of polluted air is shown. The apparatus is then left for one week. After this period, the gas volume in the measuring cylinder is $122\,\text{cm}^3$. What percentage of oxygen is present in the polluted air, correct to the nearest whole number?
- A19%
- B21%
- C28%
- D81%