But for his help, we wouldn't be working now. 这道题目是想考查虚拟语气。考查与 “现在正在做某事” 相反的虚拟语气,如果改用 would work, 则是指“将来”,无法体现出现在正在做。不过,句子编的不好,选用 work 这个单词很蹩脚。我重新设计一下: But for his help, we would be suffering a loss now. But for his help, we wouldn't be having a good time now.
but for 要不是...的话,表示与事实相反的假设,要不是他帮忙,我们现在还在忙着呢。由于他的帮忙,我们的活干完了。work为动态动词,表示事件意义,在说话时的现在now 我们实际不是正在干活,要不是他帮忙,我们现在还在干活呢。所以,这个虚拟语气必须用进行体,必须用情态动词过去式,所以would be working是正确答案。你对now的理解是错误的,对出题人的意图理解错误,所以考试你会丢分的。