分析：he will be back意义不完整，应加"什么时候"的含义才能表达idea的全部内容，因此应用when引导同位语从句。

例2：I have no impression how he went home, perhaps by bike.

分析：he went home意义不完整，应加"如何"的含义才能表达impression的全部内容，因此应用how引导同位语从句。

4. 当主句的谓语较短，而同位语从句较长时，同位语从句常后置。

如：The thought came to him that maybe the enemy had fled the city.

　　他突然想到敌人可能已逃出城了。

5. 把握同位语从句和定语从句的区别，明确同位语从句和相似从句的界限。

　　同位语从句和定语从句相似，都放在某一名词或代词后面，但同位语从句不同于定语从句。同位语从句对名词的内容进行补充说明，是名词内容的体现；定语从句说明先行词的性质与特征，与先行词是修饰与被修饰的关系。

　　引导同位语从句的that 无实际意义, 不作从句的任何成分, 不能省略，而引导定语从句的that 作从句的某个名词性成分, 如果that在定语从句中作宾语还常常省略。

　　任何一个代名词都可作被定语从句修饰的先行词，但只有内容包含性名词如fact, news, idea, truth, hope, information, wish, promise, answer, evidence, report, explanation, suggestion, conclusion, problem, question等才能够担当同位语从句的先行词。

【练习】

He told me the news that our team won the match. _______________从句

He told me the news that was very exciting. _______________从句

We are interested in the news that some foreigners would visit our school._____________从句

We are interested in the news (that/which) he told us. _______________从句