8． who/whom引导的定语从句中有插入语，而且插入语后也不用逗号分开时，很难区分它是插入语还是定语从句中的主谓结构
试比较：Mary is a girl who I believe is honest.
Mary is a girl whom I believe to be honest.
很明显，在前一个句子中，定语从句who I believe is honest中I believe是插入语，因为去掉后，语法或意义均成立，who在句中作主语，不能换用whom；而在后一个句子中，不能把定语从句whom I believe to be honest中I believe看作插入语，因为去掉后不符合语法，所以I believe不是插入语，而是定语从句中的主谓结构，whom作believe的宾语，to be honest作宾语whom的补足语。
例句： They pointed out the damage which they supposed had been done by last nights storm.（1997年第13题）
分析： 该句是复合句，其中定语从句which they supposed had been done by last nights storm中they supposed为插入语，had been done是定语从句的谓语动词。
译文： 他们指出了他们所预计的由于昨晚风暴而造成的损失。
例句： This trend,which we believe is still in its infancy, effectively began with retailers and travel providers such as airlines and hotels and will no doubt go further. （选自2011年Text 3）
分析： 该句是复合句。其中，主句的主干部分是This trend effectively began with retailers and travel providers and will no doubt go further；which we believe is still in its infancy是一个定语从句，修饰trend，we believe作插入语；介词短语such as airlines and hotels作后置定语，修饰retailers and travel providers。
译文： 这种趋势事实上起始于零售商和像航空公司、酒店等旅游服务供应商。尽管我们相信它目前仍处于起始阶段，但很有可能将会得到进一步发展。