1. 哪怕你问一千一万个人，一千一万个回答都是——强调句。that既不引导定语从句，也不引导时间状语从句。因为这里的时间状语是midnight.
2. 但如果这样改：It was midnight "when" I went home. 那么when引导了定语从句。
3. It is that 确实既可做强调句，也可做定语从句。分析方法——看that后面的句子是否主语或宾语齐全。
例一：It is Dota that he plays a lot. （Dota魔兽争霸）
that 后句子缺少宾语。判断that充当he plays的宾语，同时整句话是定语从句修饰Dota.
例二：It is his heart that warms me.
that后句子缺少主语。判断that充当warm me的主语，同时整句话是定语从句修饰heart.
例三：It was much money that he gave me.
give sb sth或give sth to sb结构，sb间接宾语，sth直接宾语，这是大学语法中的双宾语。
所以that充当gave的直接宾语，同时整句话是定语从句修饰money.
例四： It was midnight that I went home.
that后面主谓宾齐全了。所以这是强调句，如果去掉it was that，midnight就是时间状语。
4. 再说说when引导的时间状语从句和定语从句吧。方法就是——看when之前有没有先行词，例如time，day，year等。
例一： When I finished the work, it was midnight. 时间状语
例二：The moment/time when I finished the work, it was midnight.
看到when前面的mnt/time没，这就是先行词。所以when 做I finished the work的时间状语，同时整个句子做定语从句。
例二：The best day in my life was (the day) when I got married.
when 做I got married时间状语，同时整个句子做定语，修饰先行词day。
注意一个句子： It is Sunday （？） I love most.
因为I love 缺少宾语，所以（）里填that，同时that引导定语从句。不要被sunday迷惑了。
