How to fill in the void

In HTML, I would like to have something like this:

A man, a ____, a channel, panama.

I do not want underscores / underscores to be really a text entry box. What would be a good way to mark this in HTML so that it would be accessible, for example, to a screen reader? And although it is not necessary, if it is possible to say that the underline is four characters long, so much the better.