Question

they (know)each other since they (begin) to work in that factry.

请问正确时态是什么呢？1. knew. began. 2. have known. began. 3. had konwn. began.请解释一下好吗！

Answer 1

have known, began
since后面嫌凯毫无疑问过去时，“芹镇唤旅拦从、、开始就认识”持续到现在，主句用现在完成时
had known 过去完成时，表示“过去的过去”例如“they had known each other before last year"

Answer 2

2
在这里since从句后面谓语动词用一般过去时，主句用现在完成时
这里有一些例句，可以旦模氏看一下然码誉后理解一下
1) since +过去一个时间点 (如具体的模散年、月、日期、钟点、1980, last month, half past six)。
I have been here since 1989.
2) since +一段时间+ ago
I have been here since five months ago.
3) since +从句
Great changes have taken place since you left.
Considerable time has elapsed since we have been here.
4) It is +一段时间+ since从句
It is two years since I became a postgraduate student.

Answer 3

1
verb tense agreement, 都是过去式

had known = 知道一件事