With an E1 PRI the D-channel is always timeslot 16. Therefore, when only 12 B-channels are requested you must configure 1-12 for bearer traffic and still add 16 for signalling. The correct command under the E1 controller is controller E1 x/x/x pri-group timeslots 1-12,16 service mgcp (or isdn)
Option C is the only choice that includes exactly 12 bearer timeslots plus the mandatory D-channel, satisfying both the hardware change and the 12-timeslot requirement.

A. Lists timeslots that omit 16; without the D-channel the PRI cannot come up.
B. Specifies only 1-12, still missing 16, so no signalling channel.
D. Includes 1-13,16, giving 13 bearer channels—does not meet “12 timeslots” requirement.

1. Cisco IOS Voice, Video, and Applications Command Reference, “pri-group” command – “For E1, timeslot 16 is the mandatory D-channel.” (Cisco Doc ID: c80-743266-05, Section “pri-group”, p.3)

2. Cisco Voice Gateways and Gatekeepers, 2nd ed., Cisco Press, 2013, Chapter 3 “T1/E1 PRI Configuration”, pp. 101-103 – Example shows “pri-group timeslots 1-10,16” for partial E1 PRI.

3. Cisco IOS XE Gateway Configuration Guide, Release 17, “Configuring E1/PRI” – Example 7-2: “controller E1 0/0/0 … pri-group timeslots 1-23,16” (mandatory inclusion of 16).