Right answer
serio
In this exercise, Julieta and Nicolás are being described using two different adjectives. So the adjective that describes Julieta is graciosa (funny). It is given in feminine and singular form because adjectives must agree with nouns they describe in both gender and number, that is, Julieta is a feminine and singular noun. From the list, the only adjective that is related to the one that describes Julieta is serio because this is the opposite characteristic of being funny, that is, serio means serious.