Uranium-238 (U-238) decays into lead-206 (Pb-206). Which of the following is a true statement?
A. Pb-206 is the parent, and U-238 is the daughter.
B. U-238 is the parent, and Pb-206 is the daughter.
C. A rock sample containing a relatively large amount of U-238 is old.
D. A rock sample containing a relatively small amount of Pb-206 is old.