The energy changes taking place in a power station that burns fossil fuel may be represented as shown. chemical energy $W \rightarrow$ thermal energy $X \rightarrow$ electrical energy $Y$ Which expression represents the efficiency of the power station?
- A$\frac{Y}{W}$
- B$\frac{Y}{(W+X)}$
- C$\frac{Y}{X}$
- D$\frac{Y}{(W+X+Y)}$