wzc的口语太糟糕了，每次讲题的时候读单词总是要被一次次订正发音。
他立志一定要练好口语，于是每天都挑选一段文章来进行口语练习。
今天wzc挑选的文章是这一段:
Zhou Yu is handsome,and he is good at music.
He is strong too.People said that Zhou was able to find something wrong in wrong songs.When he was young,he made friends with Sun Ce (the son of Sun Jian) .He got married with Miss Qiao at the age of 24.
Zhou is very clever,and did well in war.Soldiers said he was elegance and generous.
In 208 A.D.He won the war at Chi Bi.Later,he wanted to occupy the land belonged to Cao Cao.Sadly,in December of 210 A.D. he went away in Ba Qiu because of illness.He was only 36.
在练习完之后，wzc突然想知道，这篇文章里，26个英文字母有哪些是没出现过的？