1．feel, hear, listen to 等感观动词和 have, let , make等使役动词后的补足语，在主动语态中，不定式不带to；在中，则必须带to。如：
I often hear him sing the song. / He is often heard to sing the song.
2. 不定式短语位于but, except, besides后时，如果这些介词之前有行为动词do 的各种形式，那么，这些介词后的不定式不带to，否则要带to。如：
She could do nothing but cry. / It has no choice but to lie down and sleep.
Have you got a key to unlock the door? (A key unlocks the door.)
I have got a letter to write.( I write a letter.)
The book is difficult to understand.( to understand the book)
（二） 动词 -ing形式
1． 不定式和动词 -ing形式都可以做主语，动词 -ing形式做主语表示一般或抽象的多次性行为；不定式做主语往往表示具体的或一次性的动作。如：
Playing with fire is dangerous.（泛指玩火) / To play with fire will be dangerous.（指一具体动作）
2． admit, appreciate, avoid, consider等动词后一般用动词 -ing形式做宾语。
3． 在allow, advise, forbid, permit等动词后直接跟动词作宾语时，要用动名词形式；如果其后有名词或代词做宾语，然后再跟动词作宾语补足语时，其宾语补足语用带to的不定式。如：
We don’t allow smoking here. / We don’t allow students to smoke.
1. Every detail should be thought of ______ that nothing bad will happen during the Olympics.
A. make sure B. to make sure
C. making sure D. be made sure
2. I think ______ at the Net-bar will surprise Aunt Kate.
A. your being B. you are
C. you being D. you to be
3. —Did that book give the information you need?
—Yes, but ______, I have to read it entirely.
A. for finding it B. to find it
C. finding D. finding it
4. — Did you enjoy your visit there?
— Yes, but I’m very sorry ______ so soon.
A. for leaving B. of leaving
C. to leave D. to have left
5. The professor spoke slowly enough to make his speech easy ______.
A. follow B. to follow
C. followed D. following
6. — I thought you had planned to practise the piano today.
— No. I did nothing but ______ computer games all day.
A. play B. to play
C. played D. playing
7. It is I, ______, that ______ blame for the fault.
A. not him; is to B. not he; is
C. not he; am to D. not him; are to
8. It is important for parents and young people to learn how to get through to each other and develop skills in understanding and ______ understood.
A. being B. be C. are D. to be
9. We still have many difficulties ______ in our socialist construction.
A. to overcome B. to be overcome
C. overcome D. to have overcome
10. The lost child desired nothing but ______ home to see his parents.
A. go B. to go C. going D. went
11. He was lucky enough ______ when he cheated in the exam.
A. not to be seen
B. to not have been seen
C. not to have been seen
D. to not be seen
12. Mrs Harley has a habit of asking questions ______.
A. but then not listen to the answers
B. and then not listen to the answers
C. but then not listening to the answers
D. and then doesn’t listen to the answers
Keys： 1-6 BABDBA 7-12 CAABCC