题目

阅读理解Academic learning isusually in the spotlight at school, but teaching elementary-age students softskills like self-control and how to get along with others might help to keepat-risk kids out of criminal trouble in the future.Once a program called FastTrack was started in the early 1990s for more than 7,600 children of 55 schoolsin America. They were identified by their teachers and parents to be at highrisk for developing aggressive behavioral problems. The students were randomlydivided into two groups; half took part in the intervention, whichincluded a teacher-led curriculum, pare 四面体内切球与外接球的半径分别为r和R，则r∶R＝ [　　] A．1∶2 B．1∶3 C．1∶4 D．1∶9