阅读下面短文，从每小题A、B、C、D四个选项中，选出能回答所提问题的最佳答案。
C
In America, boys and girls often join clubs. The members of a club work together. They also learn certain skills and share good times.
Many boys belong to Boy Scouts. Boy scouts enjoy hiking and camping out together, and they learn many things. Scouts learn safety rules, first aid, and what to do when in danger. Members have a chance to learn outdoor living. They learn to build fires and cook out in the open.
Girl Scouts and Camp Fire Girls are clubs for girls. These two clubs give their members a chance to have fun and learn. The girls in a group take trips, have parties and go hiking and camping together. The Camp Fire Girls earn honor beads( 荣誉珠) for learning such skills as swimming and cooking. The Girl Scouts earn badges(徽章).
Both boys and girls can be members of 4-h clubs, Children who live in either the city or the country may belong to 4-h. A project such as raising a pig or a calf can be carried on only by farm children, while city children can take part in gardening and cooking projects.
In all these clubs the boys and girls learn to be good and useful citizens.
发生，
所得结构简式有人写出下列几种，其中不可能的是
④
