A' promises 'B' to drop a prosecution which he has instituted against 'B' for robbery and 'B' promises to restore the value of the things taken.
A. The agreement is void, as the consideration for it is unlawful
B. The agreement is void as the value of the things taken in uncertain
C. The agreement is void, as its object is unlawful
D. The agreement is void, as the object of it is illegal