一个句子有且只有一个谓语动词,因此在句中充当除谓语以外的句子成分的动词形式叫做非谓语动词.非谓语动词分为三种形式：不定式、动名词和分词（分词包括现在分词和过去分词）.大体来说作状语的情况：主动doing,被动done,表目的to do；作宾语（包括介宾）主动doing,被动done,未做to do;having done表示非谓语动作先于谓语动词发生
Prices of daily goods ______ through a computer can be lower than store prices.
A are bought B bought C been bought D buying.
答案：B
When I got back home I saw a message pinned to the door ______ “Sorry to miss you; will call later.”
A read B reads C to read D reading
答案：D
The problems _ at the meeting
tomorrow are really hard to solve.
A.discussed B.to discuss
C.to be discussed D.discussing
答案：C