--Don't forget to have this machine fixed this afternoon, Darling

--Oh, you reminded me of what I otherwise         .

A. may have forgotten B. must have forgotten

C. had forgotten          D. would have forgotten

我认为答案C为错误。D为正确答案。

otherwise在此意为：used to state what the result would be if something did not happen or if the situation were different （《牛津》） 即如果你没有提醒我的话。所以，otherwise所在的分句必须使用虚拟语气。事实是你一分钟前提醒了我，我一分钟前想起了我该做某事（这让我没有忘记应该做某事）。与事实相反的假设是，如果不是你一分钟前提醒了我，我当时还想不起来要作某事。所以这个句子表达的逻辑是：

If you hadn't reminded me, I would have forgotten the repairing.