Merging a part of SVN repository to another repository with history

I have to svn repositories , lets say A and B. I want to add some of the directories of the B into A along with history.Is it possible to do that. To make more clear, following is the scenario.

    repo A                                repo B
       \branches                          \branches 
             \sub-branch1                      \sub-branch B1
              \sub-branch2                      \sub-branch B2 
       \trunk                             \trunk 

What i would like to do is, add sub-branch2 in the branches of repo A. How could do it?

thanks in advance