since加句子是什么时态

　　since的例句：

　　Things have changed since I was a lad。

　　从我幼时至今，一切都发生了变化。

　　She's lived there since before the war。

　　她从战前起就一直住在那里。

　　I've done nothing much since this morning。

　　自从今天上午我什么都没做。

　　Since losing my job I've been a vegetable。

　　失业以来我感到百无聊赖。

　　It was the worst flood since records began。

　　这是有记录以来最严重的水灾。