Which action can congress not preform, according to the constitution?

this answer is correct
appointing a new justice to the supreme court to fill a vacancy

The police of a resort town discovered that a well-known cat burglar was currently living in town under an assumed name. to try to catch her in the act of burglary, an undercover officer approached the burglar with a plan for a burglary. the undercover officer told the burglar that he knew who she was and that he had a plan to steal jewels from someone staying in one of the town's resorts. the burglar initially refused the offer; however, after lengthy cajoling, she finally agreed to the plan. as the time for the burglary drew near, the burglar had second thoughts. three hours before the theft was scheduled to take place, the burglar called the police and told them of the plan. she told them that she was not going to show up, but that her cohort (the undercover officer) would be there, and told them how to recognize the undercover officer. is the burglar guilty of conspiracy at common law?