复合不定代词是由some-,any-,no-,every-加上-one,-body,-thing所组成的不定代词.复合不定代词包括： something（某事物）, somebody（某人）, someone（某人）, anything（任何事物）, anybody（任何人）, anyone（任何人）, nothing（没事物）, nobody（没人）, no one（没人）, everything（一切事物）, everybody（每个人）, everyone（每个人） 共十二个.
Someone is reading books in the library.
Are you going to buy anything?