通过对as比较结构的学习，我知道了第二个as在它引导的句子里势必会作一个成分，但在某些as结构里，它后面甚至不是一个句子，而是一些名词，尤其是时间名词。 / He walked as far as the gate. Fields of corn spread out as far as the eye could see. / Inflation could fall back into single figures as early as this month. / Their forefathers had come to this island as far back as five hundred years ago. 对这种结构，只有把第二个as当作介词理解才可以吗？如果这样，那还可以称其为"as比较结构"吗？