对于某些“be+形容词+to do”结构，当其中的不定式与句子为被动关系时，不定式习惯上要用主动形式表示被动意义。这类形容词以easy和difficult为代表，主要包括awkward, convenient, dangerous, difficult, easy, hard, impossible, interesting, nice, pleasant, safe, tough, tricky, unpleasant 等。如：
The sentence is easy to translate. 这个句子很容易翻译。
The work is difficult to do. 这项工作很难做。
The river is dangerous to swim in. 在这河里游泳很危险。
Your writing is impossible to read. 你的书写没法认。
Do you think the water is safe to drink? 你认为这水喝起来安全吗?
Volleyball is very interesting to watch. 打排球看起来很有意思。
A man so difficult to please must be hard to work with. 一个如此难以取悦的人一定不好共事。
A foreign language isn’t by any means (=is by no means) easy to master. 要精通外语绝对不是件简单的事。
His style may be simple, but it is pleasant to read. 他的风格虽然单一，但读起来仍令人愉快。
有少数用于类似结构的形容词(如fit, ready, free等)，其中的不定式用主动式和被动式均可。如：
The water is not fit to drink [to be drunk]. 这水不适合饮用。
The letters are ready to post [to be posted]. 这信已准备好可以寄了。