追问:2016/05/12 13:53

为什么跟这些形容词就必须得用主动表被动呢

    【答】可能是与这些词的惯用法有关。例如以下内容出自《牛津英语用法指南》第三版

284.4节，其中的动词不定式都是用主动表被动：

    在一种特殊结构中，有些形容词可以与动词不定式连用，此时，句子的主语实际上是动词不定式的宾语。这样的形容词有 easy, hard, difficult, impossible, good, ready 以及 enough 之前和 too 之后的形容词。

    He's easy to please . (= To please him is easy . It is easy to please him .) 讨好他很容易。

    Japanese is difficult for Europeans to learn . ( = It is difficult for Europeans to learn Japanese .)对欧洲人来说，学日语很难。

    His theory is impossible to understand .( = It  is impossible to understand his theory .)他的理论人们无法理解。

    Are these berries good to eat ? 这种莓子好吃吗？

    The apples were ripe enough to pick . 苹果够熟了，可以摘了。

    The letters are ready to sign . 这些信可以签字了。

    The box was too heavy to lift . 箱子太重，拿不起来。