英语四、六级考试语法精要解析：不定式7

　　7. 某些动词后的不定式作宾语补足语时，不定式不带to，这些动词是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.