Which three statements about bidirectional PIM are true？（）

• A、Traffic for a bidirectional group flows along the one shared tree and simultaneously utilizes multiple paths in a redundant network topology
• B、It does not require any traffic signaling in the protocol
• C、Membership to a bidirectional group is signaled using explicit Join messages
• D、It maintains source-specific forwarding state
• E、It reduces memory， bandwidth， and CPU requirements