The given relationship is:

D d a : a D D : : R r b : ?

To find the option that satisfies the relationship, let`s analyze the given pattern.

In the first set, the relationship between the letters is as follows:

D d a : a D D

The pattern here is that the letters are reversed. So, in the second set, we need to reverse the letters again.

Thus, the second set should be:

a D D : D d a

Now, let`s look at the third set:

R r b : ?

To follow the pattern observed in the first two sets, we need to reverse the letters:

b r R

Therefore, the option that satisfies the relationship is "b r R".

The closest option given is "b R R"