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.