Answer:
B. The safari stopped at an oasis, a moist, fertile spot in the desert.
Step-by-step explanation:
An appositional phrase is one that explains a term that has been spoken before. On the basis of this, we can conclude that the sentence that presents an appositional phrase is "The safari stopped at an oasis, a moist, fertile spot in the desert," where the phrase "a moist, fertile spot in the desert" explains the word "oasis".