Tom once said something I think is appropriate as we come to the conclusion of our visit together.

【答】你的判断是对的。本句漏掉了作主语的关系代词that。I think在定语从句中充当插入语。这是一个口语的句子，出错的可能性很大。句子有两种改法：

1. Tom once said something that I think is appropriate as we come to the conclusion of our visit together.

2. Tom once said something. I think it is appropriate as we come to the conclusion of our visit together.

【语法知识】

有时，定语从句的关系词与从句中的句子成分之间，插入类似I think, I know, he believed, he guessed, we expect以及I am sure, they say等插入语，这种定语从句被称为复合式定语从句。同理，关系代词作从句的主语时，仍然不可省略。例如：

She had a book which she believed was bought by her father at a dear price.她有一本父亲送她的书，她相信是父亲花了大价钱专门买来送她的。

She has an adopted child who she says was an orphan.她有一个养子，据她所言，这个孩子以前是个孤儿

Can you mention anyone that we know is so talented as he?在我们认识的人中，你说还有谁像他一样有才华？

She is the only girl that I know can play the guitar.她是我所认识的唯一会弹吉他的女孩。

Jocelyn is the only person who we expect will win.乔斯林是我们期望唯一能胜的人。

Many college students have mastered computer, driving and foreign languages,which we all know are the most important things in today's society.

很多大学生都掌握了计算机、驾驶和外语，我们都知道这些在当今社会是非常重要的。