There is not much to choose between men.

【答】much 除了是限定词外，还可以是名词或代词，可以充当句子的主语和宾语。你的句子中，much充当了主语。

They have done much to advance the cause of peace in the world.  他们已经做了大量工作来促进世界和平事业。（作宾语）

Much has been written on the subject pro and con. 对那问题已有很多赞成和反对的文章。（作主语）

I have much to do to pay my monthly bills.  我应付每月的开支不是容易的。（作宾语）

There is much to eat at the party.  聚会上有很多吃的。（作主语）