Two genes (R or r) and (D or d), each with a dominant and recessive allele, are
inherited independently of each other. Which of the following combinations
could result in gametes of a plant with an Rr Dd genotype?
A. RD and rd
B. DR, Dr, Rd, dr
C. DD, Dd, dd, RR, Rr, rr
D. Rr and Dd