Read the sentence.

when she arrived at the concert hall, the singer walked through a crowd of cheering fans.

which word is a preposition?

she
at
walked
crowd

At is your answer

Explanation:

  Preposition is a word governing, and usually preceding, a noun or pronoun and expressing a relation to another word or element in the clause, as in “the MAN on the platform,” “she arrived AFTER dinner,” “what did you do it for ?”.

Also, prepositional phrases are in, before, after, at, down, across, inside, outside, between, by, behind, on, by, under, around, down, into, against, near, through, to, etc...

Just think of "Sammy the sidekick is ___ the tree." Sammy the sidekick is AT the tree.

Hope this helps you understand it.

B) at.

Explanation: a preposition is a word governing, and usually preceding, a noun or pronoun and expressing a relation to another word or element in the clause (some prepositions are: in, against, before, after, at, from, into, on, to, etc). In the given sentence, the word that represents a preposition is "at" (corresponding to option B). The other options are incorrect because "she" is the subject of the sentence (and a pronoun), "walked" is a verb and "crowd" is a noun.