The effect that this repetition by Gilgamesh has is: It creates a rhythmic pattern that the audience can follow, and it signals that the audience will hear a new dream.
Repetition is a rhetorical device that is used to stress something that the writer wishes the audience to be aware of.
In the story, the repetition of the sentence, "Enkidu, dear friend, I have had a dream" alerts the reader to a new dream that will be told by Gilgamesh. It also forms a sort of rhythm throughout the story.
So, option B is right.
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