注意事项：     不定式：
　　1． “to” 是不定式符号还是介词，下列短语中的to 都是介词。

　　agree to object to close to , come to , lead to , refer to ,

　　equal to , familiar to , point to , thank to , devote to , next to , belong to , be used to , look forward to

　　2． 带to 还是不带to

　　I have no choice but to give in

　　I cannot do anything but give in

　　I saw him enter the classroom .

　　（ 但是： He was seen to enter the classroom .）

　　3． 动词不定式逻辑主语是由for 作为标记的。但是有时用of .

　　区别：当使用for时，句中形容词修饰的是不定式；而用of时，句中形容词修饰逻辑主语。

　　It’s necessary for you to study hard .（necessary 修饰 to study hard，表示学习努力是有必要的）

　　It’s foolish of him to do it .（foolish 修饰逻辑主语him）

　　与of 连用的形容词有：

　　good, kind , nice , wise ,clever , foolish , right , wrong , careful , careless , polite , …

　　与for连用的通常是一些表示可能性、难易程度、必要性等含义的形容词：

　　possible，impossible，easy，hard，difficult，necessary，…

　　4．后接不定式作宾语的动词有：

　　want , hope , wish , like , begin , try , need , forget , agree , know , promise , teach , refuse , help , arrange , dare , decide , determine , fail , manage , offer , prepare , continue , ask , mean , choose , expect etc.

　　需要宾语补足语的动词不能用动词不定式直接做介词的宾语，而要用it做形式宾语。例如：通常不说We think to obey the laws is important . 而说We think it important to obey the laws .
1.______ more attention,the trees could have grown better.
  A.To give B.Having given C.Given D.Giving

  2.The first textbooks ______ for teaching English as a foreign language came out in the 16th century.
  A.to be written B.written C.being written D.having written