A Girl Runs Around a Circular Track of Radius R $\pi$

Multiple Choice

A girl runs around a circular track of radius R with a constant speed v. At the moment the girl has run half of the track, the magnitude of her average acceleration is

A) v²/ $\pi$ R.
B) $0$
C) 2v²/R.
D) 2v²/ $\pi$ R.
E) v²/R.