When he came in, which is not a right time, he was pushed by a man.请问老师这里which是指代的从句吗？which可以指代从句吗？

——没错。which 指代时间从句。

He wrote a letter that had been tainted, which made him unhappy.这里指代的是定语从句吗？

——不对。which 指代前面整个句子。

He had worked for a while, which made him at the hospital, which his mother worried.这里第二个which 指代的是前一个定语从句吗？

—— 这个句子结构和语义，都不合理。worked for a while ----- made sb. at the hospital（make 有这个用法吗）—— worried 是及物动词？