▲since 表示“从过去一直持续到现在”（所通常连用现在完成时），是指从过去一直到现在的一整段时间，即所谓的时间段。例如：

He has been living in Leeds since 1998. 他从 1998 年起就住在利兹。

We’ve known about it since May. 我们从 5 月份起就知道这件事了。

We’ve been waiting here since two o’clock. 我们从两点钟开始就在这里等了。

I’ve been on the road since 5:00 a.m. this morning. 我从今早 5 点起就一直在路上。

The factory has been here since the 1970s. 这家工厂从 20 世纪 70 年代起就在这里了。

The divorce rate has risen steadily since the 1950s. 20 世纪 50 年代以来，离婚率在持续上升。

▲after 表示“在……之后”，并不表示持续到现在，可能是指时间点，也可能是一个时间段（可能持续到现在也可能不持续到现在，after 并不作任何暗示；所以通常不与现在完成时连用）。比如：

He became quarrelsome after drinking too much. 他喝醉了就要找人吵架。

She went off in a huff after losing the game. 她输了比赛，气呼呼地走了。

Three athletes were sent home after failing drugs tests. 3 名运动员因未通过药检被遣送回国。

I had terrible pain in my guts after eating too many plums. 我李子吃得太多了，肚子疼得厉害。

The car wouldn’t start after standing outside all week. 汽车在露天停放了一个星期，已经发动不起来了。

He choked on his own blood after being shot in the throat. 他的喉咙中弹，鲜血呛得他透不过气来。

Two survivors were cut free after being trapped for twenty minutes. 两名幸存者受困 20分钟后获救。