A.Twenty bytes of header will be replaced with five bytes. 
B.If the IPSec transform set includes Authentication Header, the receiving IPSec peer will discard the packets. 
C.The IPSec packets will be dropped by Router A's compression logic.
D.The voice packets will not be compressed.

A.A voice packet is sent via multiple fixed-length cells; a portion of the last cell is padding, requiring more bandwidth.
B.ADSL typically uses PPPoE encapsulation, which adds additional overhead to each voice packet.
C.A voice packet is sent via multiple fixed-length cells; each cell has about 10% Layer-2 header overhead. 
D.IPSec requires additional overhead for the header and hash. 
E.ADSL carrier band requires additional bits to be carried over the wire to the DSL Access Concentrator.