$(6$ points$)$ A $70$ kg student initially runs toward the north with a speed of $3\mathrm{.}0\frac{m}{s}$ and suddenly makes a turn to run toward the east with a speed of $4\mathrm{.}0\frac{m}{s}.$ The process takes $0\mathrm{.}5$ seconds. The magnitude of the average force involved in the turn is

A$.0$ N $.$

B$.140$ N $.$

C$.700$ N $.$

D$.980$ N $.$

E$.$ None of the above.