1）感官动词的宾语补足语中不带to
see　hear　watch　notice　feel　observe
2）使役动词的宾语补足语中不带to
let　make　have
例句
a. The teacher has us write a composition every week.
b. I saw a man enter the shop.
c. To calm the patient, the dentist offered him a shot of whiskey. The man tossed it down（一饮而?。? then had another. “Now,” said the dentist,“got your courage back?” “Yeah,” snarled（咆哮） the patient. “And I’d like to see anybody try to touch my teeth.”
为使病人平静下来，牙医给了他一杯威士忌。该男子一饮而尽，接着又喝了一杯。牙医说：“现在，你不再害怕了吧？”病人咆哮道：“是的，我倒要看看谁敢碰我的牙齿。”
上述动词若转换为被动结构时，其后不定式需将to还原回来：
d. A man was seen to enter the shop.