①A∪B={1，2，3，4，5，6，7}；②A∩B=∅；③A中的元素个数不是A中的元素；④B中的元素个数不是B中的元素．

若集合A含有2个元素，则满足条件的A有____个．

   A hobby is a special interest or an activity that people like to do in their free time．Most people in Britain have their own____(hobby)．

   Some people train dogs to race or keep pigeons(鸽子)____(carry)messages．Some people are crazy about plants．They put many  ____(kind)of beautiful flowers in their kitchens and living rooms．____(other)are mad about their cars or motorbikes．They spend their weekends____(wash)them，painting them and trying 

____(make)them go faster．Children and teenagers are  ____(interest)in collecting things．They collect stamps，postcards or pictures of a favourite pop star．

   ____(learn)something new is also people's hobby．Some people go to evening classes to learn  ____(dance)，body building，bread making and so on．Some people learn these things by ____(they)．