Tried to find a tool which can extract a page from a multi-page .djvu file, but failed. djvutoy in Windows may do that job, but no counterpart found in Linux.
So I use a circuitous way to do this job:
ddjvu -page=3 -format=tiff doc.djvu page.tiff cjb2 page.tiff page.djvu
Then you can use page.djvu as a single-page .djvu file, which can be used in djvm, such as:
djvm -i doc.djvu page.djvu 10
This sets page.djvu as the 10th page in doc.djvu.