Answer:
B). Ian just got back this afternoon from his trip to Europe, and he is happy, excited, but is exhausted.
Explanation:
The correct version of the given sentence is displayed in option B as it involves the repetition of verbs that proposes parallel construction of the sentence that organizes and balances the description provided. As we know that coordinating conjunctions like 'but' employs a similar form of verbs after it(as applied previously in the sentence) in order to offer a parallel meaning to the sentence. Similarly, option B appropriately follows('is exhausted') the previous verb 'is happy'. Thus, option B is the correct answer.