Not sure which word is bolded, but I can still help you out. There are two pronouns in this sentence: we and us.
If we is bolded, the answer is C. nominative case. These pronouns are often the subject of a sentence.
If us is bolded, the answer is A. objective case. The object of a sentence receives the verbs attention. In this sentence, you ask "What is surrounded?" to understand that us is objective case.
Just so you know, possessive case is when the pronoun owns something. For we, the possessive pronoun is our. We went home to our house.