B【句意】如果没有你的帮助,我们不会克服那些困难.
【解析】根据句子结构,我们可以看出逗号后面是使用了虚拟语气的主句,因此,须填入表示与过去情况相反的虚拟条件句,"if it were not for …"这一结构表示同现在事实相反的假设,意为"如果不是……",例如：If it weren't for his wife's money,he'd never be a director."如果不是他妻子有钱,他永远不会成为一名董事.If it were not for his help,I would never study here．如果没有他的帮助,我永远不会在这儿学习.因此,BIf it were not 错误."if it had not been for …"的倒装形式为"had it not been for …",表示与过去事实相反的假设,意为"如果当时没有……",主句谓语形式是"would ＋ have done",例如：If it had not been for Dr.Li,he would have died of smallpox.如果当初不是李医生的话,他已死于天花了.Had it not been for his carelessness,the project wouldn't have failed.当时如果不是他粗心的话,这项工程不会失败.因此,B.Had it not been正确,A.Had it not错误（如果后跟been,就是正确的了）