18. The half-life of 14C is 5730 years. A sample taken for radiocarbon dating was found to contain 56 percent of its original 14C. What was the age of the sample? (Radioactive decay of 14C follows first-order kinetics.) (A) 2.2 × 10^3 (B) 3.1 × 10^2 (C) 4.8 × 10^3 (D) 1.1 × 10^4