定语从句只用that的口诀“多少不一恰人物最序”是指定语从句必须用that的情况，当先行词是，或先行词前有几种情况时，变成了顺口溜：“多少不一,恰人物最序”。
1、表示“多少”的词，如多：many/much， 少：little/few ，如：
He has little information that is useful for our research.
他几乎没有对我们的研究有用的信息。
2、不定代词：指有all,none,every,each,everything,nothing,anything,any，如：
Is there anything that I can do for you?
有需要我帮你做的任何事情吗？
3、一：指有the one,the only,the every
He is the only child that his parents have.
他是父母唯一的孩子。
4、恰：指有just,the right,the same时，如：
He gave me the same book that he read yesterday
他给了我与他昨天读的同样的书。
5、人物：先行词既有人又有物时
He talked about the teachers and schools that he had visited.
他提到他参观的学校和老师。
6、最：先行词为最高级时
He think it one of the most wonderful films that the film company has ever produced.
他认为这是电影公司生产的最精彩的电影之一。
7、序 ：先行词为序数词时
He was the second person that told me the secret.
他是第二个告诉我秘密的人。