For a male to express a recessive sex-linked trait, he must have- A- one dominant and one recessive allele
B-two recessive alleles
C- Only one recessive allele
D- two dominant alleles

Ihave no idea how to solve these. plus there's another question that is 2) a 10 kilogram meteorite is collected in space and brought back to earth. it is composed of 1.25 kg of uranium-238 and 8.75 kg of lead-206. how many u-238 half lives have passed? what is the approximate age of the meteorite?