Refer to the exhibit.

I understand your reasoning, but I think option C is still the correct answer. The question is about Cisco Webex calling, which is a cloud-based service that provides voice and video calling features. Cisco Webex calling does not use UDP port 5062 for SIP signaling, but TCP port 8934. The Cisco Unified Border Element (UBE) is a local gateway that connects the PSTN to the Webex calling service. The UBE uses UDP port 5062 for SIP signaling only between itself and the PSTN, not between itself and the Webex calling service. Therefore, opening UDP port 5062 on the firewall will not help Alice to reach Charlie using Webex calling.

You can find more information about Cisco Webex calling and Cisco Unified Border Element here:

https://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cucm/admin/12_5_1/systemConfig/cucm_b_system-configuration-guide-1251/cucm_b_system-configuration-guide-1251_chapter_0100110.html

https://www.cisco.com/c/en/us/products/unified-communications/webex-calling/index.html