元音发音时间的规则是?答:总结一下:oo读成短元音[u]的单词有:good/goods,wood,foot/footprint,childhood/boyhood/adulthood,stood/understood,classroom/sitting-room/reading-room,look/book/took/cook/cooker.oo读成长元音[u:]的单词有:fool/foolish/school/cool/pool/tool,food,noodle,too/zoo,room/doom,boot,shoot,moon/...