Choose the appositive or appositive phrase in the sentence. if the sentence has no appositive or appositive phrase, choose none.

nelson, though he is young, is widely admired for his knowledge of modern art, a challenging field of study.

none

of modern art

a challenging field of study

for his knowledge

Aman lives on the twelfth floor of an apartment building. every morning he takes the elevator down to the lobby and leaves the building. in the evening, he gets into the elevator, and, if there is someone else in the elevator -- or if it was raining that day -- he goes back to his floor directly. otherwise, he goes to the tenth floor and walks up two flights of stairs to his apartment.