for your help, we couldn't have succeeded.

A. If it had not been 

B.  If it were not  

C. Had it not been

D.  Were  it not

答案: 解析如下所述

A. If it had not been for your help (假如）要不是你的帮助

=Had it not been for your help对过去的虚拟和假设

B.  If it were not  for your help要不是你的帮助

=Were it not for your help对现在和将来虚拟和假设

C. Had it not been for your help要不是你的帮助

=If it had not been for your help 对过去虚拟和假设

D.  Were  it not for your help 要不是你的帮助

If it were not for your help对现在和将来虚拟和假设

备注(1)：主句为对“过去事件的虚拟”。

备注(2):虚拟条件句省略if 可以用采用倒装形式替代，

备注(3)but for +名词=without+名词=if it had not been for+名词/it were not for +名词要不是....

A:含蓄条件句：虚拟的条件不是通过条件句来表示，而是用一些词或短语，如 without, but for, or , otherwise等，这种句子叫含蓄条件句。

But for/without electricity=If it were not for electricity, there would be no modern industry.

But for/without your help=if it had not been for your help, I could not have succeeded.

But for/without your advice=if it had not been for your advice/Had it not been for your advice, we could not overcome these difficulties.

I was ill that day. Otherwise, I would have taken part in the sports meet.

（句子含有but for, without, otherwise, or 而没有if的虚拟条件句称作为“含蓄虚拟条件”如果主句和从句时间不一致称作为“错综时间虚拟条件句”）

B:错综时间条件句：（虚拟语气中，条件从句的动词动作可以和主句的动词动作时态不一致。）

从句和主句要根据各自发所生/设定的时间选用符合具体时间的虚拟语气形式 。
(1)从句表示过去，主句表示现在 
If they had stared the early morning yesterday, they would be here now.
(2)从句表示将来，主句表示过去 
If I were not to make a preparation for my experiment this afternoon, I would have gone to see the film with you last night.
(3)从句表示过去，主句表示将来 
If we hadn't made adequate preparations, we shouldn't dare to do the experiment next week.
(4)从句表示将来，主句表示现在 
If we shouldn't have an exam this afternoon, I would go shopping now.

更多的时间错综条件句如下：

If it had rained last night, the ground would be wet now. 

要是昨晚下过雨的话，现在地面就会是湿的。

You would be much better now if you had taken my advice. 

假若你当时听我的话，你现在就会好多了。

If I had not got married, I would still have been living abroad. 

如果我没结婚，我会仍然一直住在国外。

If she were trying harder, her parents wouldn’t be so anxious. 

如果她现在更用功些，她的父母也不会这么忧虑了。

If it had been raining this morning, we would have stayed home. 

如果今天早上一直下雨，我们就会待在家里了。

If you’d listened to me, you wouldn’t be in such trouble now. 

如果你听了我的话，你现在也不会有这样的麻烦了。

If it hadn’t been for her care, I should not be speaking to you now. 

如果不是她精心照料我，我现在也不会在这里和你谈话了。

If the doctor had come in time, Amy would still be alive. 

如果医生及时赶到艾米现在还会活着。

If he had received six more votes, he would be our chairman now. 

如果他多得六票，现在就是我们的主席了。

If you were in better health, we’d have let you go with us. 

你要是身体好一点，我们就让你和我们一道去了。

If I were you, I would go. 

假若我是你，我就去。

If I were not busy, I would have come. 

假若我不忙，我早就来了。

If I had been you，I’d have taken the job. 

我要是你，我就接受那份工作了。

句子的意思应该是：要是当初没有你（们）的帮助，我们就不可能成功。因此立刻可以排除B和D，他们都不属于“对过去事实相反”的虚拟语气。我觉得A和C都对，它们的区别应该是倒装与否。另外，这句话还可以说：Without (=But for) your help, we wouldn't have succeeded. 

其实, 即使考虑语体的因素，从语法上看，选 B 也是对的。参见：

http://www.yygrammar.com/Article/201509/4177.html 

另外，几位老师认为，这类句子为了保持语体上的一致性，主句和从句一定要同时用或同时不用缩略式的看法，过于“谨慎”了，其实不一致的情况也是可能的：

If it were not for the fact that he is my father, I’d accuse him in public. (麦克米伦)