The sentence which has a pronoun in the nominative case is, We aren't sure if the group is going white-water rafting or not.
Option A.
Step-by-step explanation:
When it comes to pronoun cases, there are three cases: nominative, possessive, and objective. The nominative case is mostly used when the subject of any sentence is pronoun. Nominative case pronouns includes: I, he/she, who, we, and they. For example: 'She drinks juices' here, the pronoun 'she' is the subject of the verb eats and she is the nominative case.
Similarly, in the sentence, 'We aren't sure if the group is going white-water rafting or not', the pronoun 'we' is the subject of the verb going and thus also a nominative case.