Which part of speech is the underlined word in the sentence? food is an important part of any festival. ( of is the underlined word )

a. interjection

b. adverb

c. preposition

d. conjunction

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.