the experts were now fully convinced that the animal was a puma,but where had it come from?As no pum

题目

the experts were now fully convinced that the animal was a puma,but where had it come from?As no pumas had been reported missing form any zoo in the country
but where had it come from?这里的had为什么要用过去完成时呢 ,而且come from这里的come为什么不用came?

答案

发生在过去的过去 用过去完成时 既然是过去完成时 had+过去分词 自然是had come from came 是come的过去式哦 肯定是不能用在这里的 原形come---过去式came---过去分词come