Which set of additional commands within this policy-map will improve the link efficiency on the serial interface?

This policy-map is applied to a 128-kbps serial interface in the output direction. Which set of additional commands within this policy-map will improve the link efficiency on the serial interface?

policy-map test
class voice
priority 25
class telnet
bandwidth remaining percent 20
class ftp
bandwidth remaining percent 30

A.
class voice
no priority 25
bandwidth percent remaining 25

B.
class voice
compression header ip tcp

C.
class telnet
compression header ip tcp

D.
class telnet
fair-queue

E.
class ftp
fair-queue

F.
class ftp
compression header ip

Explanation:

RTP and TCP IP Header Compression
RTP or TCP IP header compression is a mechanism that compresses the IP header in a data packet before the packet is transmitted. Header compression reduces network overhead and speeds up transmission of RTP and TCP packets.
Cisco IOS software provides a related feature called Express RTP/TCP Header Compression. Before this feature was available, if compression of TCP or RTP headers was enabled, compression was performed in the process-switching path. Compression performed in this manner meant that packets traversing interfaces that had TCP or RTP header compression enabled were queued and passed up the process to be switched. This procedure slowed down transmission of the packet, and therefore some users preferred to fast-switch uncompressed TCP and RTP packets.
Now, if TCP or RTP header compression is enabled, it occurs by default in the fast-switched path or the Cisco Express Forwarding-switched (CEF-switched) path, depending on which switching method is enabled on the interface. Furthermore, the number of TCP and RTP header compression connections was increased.
If neither fast-switching nor CEF-switching is enabled, then if TCP or RTP header compression is enabled, it will occur in the process-switched path as before. The Express RTP and TCP Header Compression feature has the following benefits:

It reduces network overhead.

It speeds up transmission of TCP and RTP packets. The faster speed provides a greater benefit on slower links than faster links.

SUMMARY STEPS
1. enable
2. configure { terminal | memory | network }
3. policy-map policy-name
4. class-map class-map-name
5. compression header ip { rtp | tcp }
6. exit