1.too /enough / so
① tooto 表示否定的意思，太而不能
eg：Heis too young to go to school.
② adj. / adv. 原级+ enough + to do，足够去
eg：Heis seven now, he is old enough to go to school.
③ so+adj. / adv.原级+ that + 从句，如此以至于，常出现在结果状语从句中。
eg：Heis so young that he cant go to school.