When STP operation is functioning normally, which statement is true about BPDUs?

A.
A bridge sends configuration BPDUs towards the root bridge every two seconds

B.
A bridge sends configuration BPDUs towards the root bridge every 15 seconds.

C.
A bridge sends a TCN BPDU to the root bridge once upon initial configuration, followed by
configuration BPDUs every two seconds.

D.
A bridge sends only TCN BPDUs to the root bridge and no configuration BPDUs.