The Radioactivity Due to Carbon-14 Measured in a Piece of a Wood

The radioactivity due to carbon-14 measured in a piece of a wood from an ancient site was found to produce 20 counts per minute from a given sample,whereas the same amount of carbon from a piece of living wood produced 160 counts per minute.The half-life of carbon-14,a beta emitter,is 5730 y.The age of the artifact is closest to

A) 5700 y.
B) 12,000 y.
C) 15,000 y.
D) 17,000 y.
E) 23,000 y.