Although/Though/Even though he was very tired, he kept on working.

出这个考题的人自己都没有搞清楚。三个连词用在这里都是正确的。even if 带有假设意义，从句谓语表示的是假设的情况。但 even though却并非如此，even though是though 或 although的强调形式。能用though 和 although的地方，就能用even though。

《朗文》even though

used to emphasize that something is true although something else has happened or is true 

Even though he’s 24 now, he’s still like a little child.

《麦克米伦》even though

used for introducing a fact that makes the main statement in your sentence very surprising

Most of us ignore this good advice, even though we know it to be true.

Even though I have a master’s degree in business administration, I can’t fill out my tax form.

《韦氏学生词典》even though

— used as a stronger way to say “though” or “although”

• She stayed with him even though he often mistreated her.

• I'm going even though it may rain.

以上三部词典中的黑体的例句中，从句表示的都是事实。