The carbon-14 activity of some ancient Native American corn was found to be 7.0 disintegrations per minute (dpm) per gram of carbon. If present-day plant life has 16 dpm per gram of carbon, how old is the Indian corn? (t1/2 = 5,730 yr)
A) 6,800 yr B) 2,500 yr C) 4,700 yr D) 10,000 yr E) 7,200 yr