A mixture containing $10\,\text{cm}^3$ of methane and $10\,\text{cm}^3$ of ethane was ignited in excess oxygen. After the products had cooled, the remaining gas was passed into aqueous potassium hydroxide. All gas volumes were taken at the same temperature and pressure. Which volume of gas was absorbed by the alkali?
- A$15\,\text{cm}^3$
- B$20\,\text{cm}^3$
- C$30\,\text{cm}^3$
- D$40\,\text{cm}^3$