[单选题]
The engine of a racing car provides a forward thrust of $800\;N$. The average of the total resistive forces acting on the car is $300\;N$ and the car covers a distance of $1.0km$ in $10s$. What is the average output power of the engine?
A. $5.0\times10^3W$
B. $8.0\times10^3W$
C. $5.0\times10^4W$
D. $8.0\times10^4W$
