which three statements are true about IS-IS adjacencies?

On a broadcast network, which three statements are true about IS-IS adjacencies? (Choose three.)

A.
Peers send full copies of databases at regular intervals.

B.
IIH PDUs are used as a keepalive mechanism.

C.
Peers can request missing link-state information.

D.
An elected DIS retains its status as long as the device remains up.

E.
Peers acknowledge receipt of link-state updates.