why he was late was (that)his alarm clock was broken.只要记得why 与 because 还有although与 but 不一起用就好了.细说的话： why he was late 是主语 was是系动词,后面应该是个事实做表语.why he was late was...我记得好像有个结构是 be+because的 那是什么啊？That is because an economy's trend growth rate cannot be measured directly.这是因为一个经济体的趋势增长率不能直接被测算。That is because different areas use different methods to find graduation rates.这是因为不同区域使用不同的方法来找出毕业率。That is because China has ceased to be merely a low-cost production centre.这是因为，中国已经不再仅仅是成本低廉的生产中心。