Answer:
The word which is the preposition in the above sentence is:
D. After
Step-by-step explanation:
A preposition is the part of speech which tells about the relation of the subject with the object in the sentence. It helps to create a link between the nouns, pronouns or the phrases in a sentence. It tells about the location, duration, and connection of the words. Usually, prepositions are placed before the nouns in the sentences. In the above sentence, the preposition 'after' tells about the time when the people went to backstage.