In grammar, the words "us" and "we" are both pronouns that replace a noun; however, these are different types of pronouns and used in different cases. In the case of "we" this a subjective pronoun which means it should be used as a subject or agent that performs the action in a sentence, while "us" is an objective pronoun and is used as an object or entity being affected by the action. This means in the case of the sentence "_____ freshmen are planning the activities" in which the word that needs to be completed appears before the verb and it is the agent that performs the action "are planning" the correct pronoun should be a subjective pronoun, as this is the type of pronoun used as a subject and therefore the word that completes the sentence is "we".
I say the answer is C because we can clearly see that the setting of the library is being observed by the character. We get a clear description of different items in the library. (Let me know how good my answer is!)
