A device has an energy input of $E$. The energy wasted by the device is $W$. Which expression represents the efficiency of the device?
- A$\frac{W - E}{W} \times 100\%$
- B$\frac{W}{E} \times 100\%$
- C$\frac{E - W}{E} \times 100\%$
- D$\frac{E - W}{W} \times 100\%$