Final answer:
The sentence that contains an idiom is 'Kara told Maria not to spill the beans about Roberto's surprise party.' The idiom 'spill the beans' means revealing a secret or confidential information.
Step-by-step explanation:
An idiom is a phrase that has a figurative meaning different from its literal meaning. The sentence that contains an idiom is 'Kara told Maria not to spill the beans about Roberto's surprise party.' Here, 'spill the beans' is an idiom that means revealing a secret or confidential information.
Learn more about Idioms in English