This development has also accelerated ____ the civilian airlines were first"deregulated(解除管制)", this is , allowed to compete with eacho otherfor more routes and passengers,in the late 1970s.[A] since[B] after我只记得since只能用于完成时，如果一个句子有主句有从句，那么这两个句子都要是完成时才可以，是这样么？1：但为什么这样我一直不理解。。。2：如果是这样，后面得句子he civilian airlines were first deregulated是过去时，也不是完成时啊。这个since在做选择题时候老错，在和它意思差不多得词选择的时候，麻烦大家不忙时候讲讲谢谢
參考答案:别浪费感情啊，没有人回答你得问题把分给我得了
