You still are worried about reading acm English problem, let me tell you a kind of very good method of Memorising Words, the root memory method,.the most interesting of the method is the prefix root. Now there are some English words to remembeand he knows some prefix root;He want to know how many words that can be remembered using each the prefix .in other words,how many words that contain the prefix ,Now to acmer you for help, can you help him?