Several years has passed since we started our middle school life.这里为什么是has passed?

题目

Several years has passed since we started our middle school life.这里为什么是has passed?
several years不是复数形式吗,为什么不是用have passed

答案

Several years 几年,属于时间作主语,英语中 时间,数量,金钱作主语都看做第三人称单数.例如：Ten years is a long time.The number of the students in our school is about 2000.Five dollars is not enough for him...