The correct answer is D. In a Versa HA active-active branch deployment, the cross-connect link between the two CPE devices is used to extend WAN transport reachability between the peers. Versa SD-WAN design documentation explains that, in an HA active-active design, a cross-connect cable between the two devices extends one device's transport VR to the other device and vice versa. For example, the documentation describes the cross-connect as extending the MPLS-Transport-VR to one device and the Internet-Transport-VR to the peer device.

In the question, there are four total WAN networks across the HA pair: INET-1, MPLS-1, INET-2, and MPLS-2. The HA active-active workflow must create separate logical subinterfaces on the cross-connect link for each WAN network so that each transport segment can be extended and kept logically separated across the two appliances. Therefore, the number of subinterfaces created on the cross-connect link equals the total number of WAN networks across the HA pair, which is four.

Options A, B, and C are incorrect because they undercount the number of required transport extensions. Two subinterfaces would only account for two WAN networks, but this design has four separate WAN transport networks.