Trains deliver coal to a power station. The table lists the quantities that describe how the power station operates: average output of the power station $P$ (unit W); number of trains each day $N$; mass of coal carried on a train $M$ (unit kg); energy released by $1\,\text{kg}$ of coal $E$ (unit J); number of seconds in one day $S$. Which expression represents the efficiency of the power station?
- A$\frac{PS}{NME}$
- B$\frac{PSN}{ME}$
- C$\frac{NME}{PS}$
- D$\frac{NM}{PSE}$