动名词、分词、不定式。
主动或被动。(doing/done, to do /to be done)发生在谓语动词之前还是之后。(doing/ having done /having been done, to do/to have done /to have been)To在什么情况下作介词，什么情况下作不定式引导词。
真题剖析
(2000) … In the inner cities of America, newspapers regularly report on newborn babies 60 into garbage bins by drug-addicted mothers.
60. A. dropped
B. to drop
C. dropping
D.drops
(2001.3) A heroin addict, for instance, leads a 59 life: his increasing need for heroin in increasing doses prevents him from working, from maintaining
relationships, from developing in human ways.
59. A. destructive
B. dissatisfied
C. damaged
D. derivative