Who loads bridge.ko modules when Linux system starts?

Question

When my CentOS Linux system starts, bridge.ko and ebtable_broute are loaded, I'd like to know which module is loading these modules.

[root]# lsmod | grep bridge
bridge                266240  0
stp                    16384  1 bridge
llc                    16384  2 bridge,stp

[root]# lsmod | grep ebtable_brout
ebtable_broute         16384  1
bridge                200704  1 ebtable_broute
ebtables               36864  3 ebtable_nat,ebtable_filter,ebtable_broute