Answer:
es
Step-by-step explanation:
Translated: Poor dear! The party is a lot of fun.
The correct answer is es since we know we must conjugate the "ser" into a present tense. From this, we have eliminated past and future tenses, and we must decide which form to use. We cannot use the yo, tu, nosotros, vosotros, or ellos/ellas/ustedes, which means we can only use the el/ella/usted form, leaving us with the answer of es. I hope this helped and please don't hesitate to ask for clarification!
Edit: I realized that there are four options: fue, ir, ser, and estuvo.
From here, our answer should be fue, since both ir and ser are verbs, and estuvo would not make sense in this context. Hope this helped!