[Boost-users] binary library result

After I built boost in Linux, I found in the lib directory there are three files for each package. For example, for system, files are libboost_system-gcc41-mt-1_35.so libboost_system-gcc41-mt-1_35.so.1.35.0 libboost_system-gcc41-mt.so Why is that? Only one file is needed in my link flag? which one? thanks, James