赖世雄教你学英语语法
时态及语态
1-16：It is+时间+since
It is+时间+since... 自从…… ＝It has been+时间+since...
例：It has been five years since I saw you last time. = It is five years since I saw you last time. （自我上次见到你，至今已有五年了。）