The reason why he missed the bus was that he got up late.

The reason why he missed the bus was that he got up late.

that引导的是表语从句，这时候一般不省略。
that在引导名词性从句的时候(主语、宾语、表语、同位语从句)，都没有实际意义，只作引导词，但是只有宾语从句中的that被省略。

a 试题分析：句意：他迟到的原因是他没有赶上火车。第一空是why引导的定语从句，why在定语从句中状语，先行词是reason；第二空是that引导的表语从句，that在表语从句中不做成分。固定句式the reason why……be that…,故选a。 点评：本题难度适中。定语从句及表语从句是高中英语语法中非常重要的内容，对它们的考查关键在于分析从句的成分，需要考生有分析理解复杂的句子结构的能力。 即学即练：the reason ______ he told me for his absence did not sound believable. a. why       b. because c. that     d. whom 解析：c。句意：他告诉我他缺席的原因很难使人相信。