Which of the following sentences has an error in agreement?

everyone should wear his or her seatbelt while flying.

flies is buzzing over the trash can.

two girls and a boy are here to deliver the papers.

did anne or her friend mary leave her wallet on the table?

i think the answer is b

kenny´s more than 25 years of relevant public service. in the army for two decades, as official representative for four years, and now for the department of state, as ambassador. this career clearly demonstrates great capacities in the public sector.