Present Perfect ：现在完成时
indicates continued action
indicate continued effect of past action
ex： He has drawn on the beach.
At the same time: She will pay you when you ask her.
After: She will pay you when you has asked her.
过去完成时Past Perfect :had + past participle
before / after
出现的时候，可以不⽤用past perfect，⽽而使⽤用simple past。因为动作的先后顺序已 经⾮非常明显
Laura locked the door before she left.
ex：Theband U2 WAS just one of many new groups on the rock music scene in the early 1980s, but less than ten years later, U2 HAD fully ECLIPSED its early rivals in the pantheon of popular music.
Conditional tense: would +verb
present+ future ( will do)
past+ conditional( would do)
The shuttle launch TOOK place flawlessly and WAS SEEN on television