expensive to buy

在英语的某些形容词之后需要用主动形式的动词不定式来作补足语，从语义上看，句子的主语便是动词不定式的宾语(参见 difficult, hard)。例如：

1. Big houses are expensive to maintain. 维护大房子是很费钱的。

2. Bob is hard to convince. $\$left\{ \begin{array}{ll}\sim \text{To convince Bob is hard.}\\ \sim \text{It is hard to convince Bob.} \end{array} \right. 鲍勃是很难说服的。

3. The house is easy to find. 这座房子很好找。

下列形容词具有以上用法：

awkward hard convenient impossible difficult nice easy pleasant