Which of the following statements regarding LSDB synchronization on an IS-IS broadcast network is true?

R2 functions as the DIS and sends Hello PDUs at an interval three times that of non-DIS routers. 

R2 functions as the DIS and does not receive PSNPs from other routers. 

R2 functions as the DIS and periodically sends CSNPs. 

R1 and R3 maintain the LSDB consistency by sending PSNPs periodically.