6. 帶疑問詞的不定式短語

　　不定式前可以加某些疑問代詞，如who、what、which,或疑問副詞，如when、where、how、why等，構成一種特殊的不定式短語，可在句子中作主語、賓語、表語或狀語等。

　　How to improve English is often discussed among the students.

　　We haven’t decided when to visit the place.

　　The most difficult thing in learning English is how to speak the language well.

　　You haven’t answered my question where to get these books.

　　7. 某些動詞后的不定式作賓語補足語時，不定式不帶to，這些動詞是feel, have, hear, let, make, notice, see, watch等。

　　Suddenly I felt the atmosphere in the room become tense.

　　I often hear them sing this song.