Which source port does IKE use when NAT has been detected between two VPN gateways?

Which source port does IKE use when NAT has been detected between two VPN gateways?
A . TCP 4500
B . TCP 500
C . UDP 4500
D . UDP 500

Answer: C

Explanation:

The IKE protocol uses UDP packets, usually on port 500 NAT traversal: The encapsulation of IKE and ESP in UDP port 4500 enables these protocols to pass through a device or firewall performing NAT

Source: https://en.wikipedia.org/wiki/Internet_Key_Exchange