A hydroelectric power station converts the gravitational potential energy of water into electrical energy. In one specific power station, the mass of water passing each unit time is $1.5 \times 10^5\,\text{kg s}^{-1}$. The water descends by a vertical distance of $120\,\text{m}$. The electrical power produced is $100\,\text{MW}$. What is the efficiency of the power station?
- A$5.6\%$
- B$43\%$
- C$57\%$
- D$68\%$