Five years has passed since we met last .为什么不用have passed?

Five years has passed since we met last .为什么不用have passed? 1.Once year(has passed)since we last met.为什么不用have passed? It has passed 10 years since we met last time. three years have passed since they met last time. one year has passed since we last met. one and a half years (have/has) passed since we last meet. ten years have passed还是has passed 2 years has passed还是have passed Several years has passed since we started our middle school three years has/have passed two years have passed 还是two years has passed Four months __ passed by since we met last time.Four months