Suppose that $C$ represents the set of all countries, $R$ represents the set of all countries that have at least one river flowing through it, $M$ represents the set of all countries that have at least one mountain in it, and $D$ represents the set of all countries that have at least one desert in it. It is given that: \[ R \cup M \cup D = C \] Which one of the following gives the set of all countries that have either a mountain or a river, but do not have a desert in it? The notation $D^{c}$ represents the complement of the set $D$ with respect to the universal set $C$.