Answer:
b. It implies that the cherry trees are a new addition to Washington, D.C.
Step-by-step explanation:
When the narrator refers to the "novel" characteristic, he/she indicates that this characteristic adds to the exclusivity of Washington D.C (and it is already pretty exclusive, since it is the capital city of U.S.). Moreover, since cherry trees are from Japanese origin, they didn't use to grow up there and these facts distinguish this city from other cities.