What is the purpose of the outside source used in this excerpt ?

Read these sentences from the first section of the article. because of this novel characteristic which singles out washington from other cities, coupled with the fact that the trees are now in full splendor, a short history of their appearance in the capital city is of interest. the first cherry trees were planted in washington by mrs. taft's request on april 4, 1909, just a month after she first made her home in the white house. what is the most likely reason why cobb includes these sentences in the first section? a- to establish himself as a credible authority on the topic of cherry trees b- to state the central idea and begin the narrative of how the trees arrived in washington, d.c. c- to create a sensory image for readers who are not familiar with cherry trees d- to build suspense as to how so many cherry trees arrived in washington, d.c.