The class is nervous about _____ first exam. Which of the following is the correct form to complete the sentence?

In this sentence, 'Its' is the correct form to indicate possession. 'Its' is a possessive pronoun that shows something belonging to 'the class,' referring to the class's first exam. It does not require an apostrophe since 'its' is a possessive pronoun, whereas 'it's' is a contraction for 'it is' or 'it has,' which is not suitable in this context. Choice 'they're' is incorrect because it is a contraction of 'they are,' which does not fit the sentence. Therefore, the correct answer is 'Its.'