Concept:The idiom "keep someone on their toes" means to make someone stay alert and ready for anything.Explanation:Someone standing on their toes is ready to move at once, so being "on your toes" means being watchful and prepared.While the soldiers were in town, people had to stay watchful and careful.The idiom does not mean running away (A), working harder (B) or being excited (D).So the visit caused us to be alert.Answer:Option C (caused us to be alert)