L2TP and GRE are both tunneling protocols that can be used to create site-to-site VPNs. However, they have some differences in how they encapsulate and transport data. L2TP is a layer 2 protocol that uses IP packet encapsulation to carry PPP frames over an IP network. L2TP does not add any additional header to the IP packet, but relies on IPsec to provide encryption and authentication. GRE is a layer 3 protocol that adds its own header to the IP packet, which contains information such as the protocol type, checksum, and key. GRE can be used to carry any type of payload over an IP network, not just PPP frames. GRE also requires IPsec to provide security for the tunnel. Therefore, the correct answer is C, because GRE over IPsec adds its own header, and L2TP does not1234 References := 1: Implementing and Operating Cisco Security Core Technologies (SCOR) v1.0 - Module 5: Secure Connectivity 2: What is the difference between L2TP vs GRE 3: GRE over IPSec vs L2TP over IPSEC 4: difference between L2TP/GRE/MPLS

Explanation
Cisco Hybrid Email Security is a unique service offering that facilitates the deployment of your email security infrastructure both on premises and in the cloud. You can change the number of on-premises versus cloud users at any time throughout the term of your contract, assuming the total number of users does not change.
This allows for deployment flexibility as your organization's needs change.

Reference:
https://www.cisco.com/c/en/us/support/docs/security/email-security-appliance/118219-configure-esa-00.html

VMware APIC is a platform that integrates with Cisco ACI to provide enhanced visibility, policy integration and deployment, and security policies with access lists. VMware APIC is a virtual appliance that runs on VMware vSphere and communicates with the Cisco APIC controller. VMware APIC allows administrators to create and manage Cisco ACI policies for VMware virtual machines and networks. VMware APIC also provides a unified view of the physical and virtual network topology, health, and statistics. VMware APIC supports the following modes of Cisco ACI and VMware integration:
* VMware VDS: When integrated with Cisco ACI, the VMware vSphere Distributed Switch (VDS)
* enables administrators to configure VM networking in the ACI fabric.
* Cisco ACI Virtual Edge: Cisco ACI Virtual Edge is a distributed service that provides Layer 4 to Layer
7 services for applications running on VMware vSphere.
* Cisco Application Virtual Switch (AVS): Cisco AVS is a distributed virtual switch that provides policy-based network services for VMware vSphere environments. References:
* Cisco ACI with VMware VDS Integration
* Cisco ACI and VMware NSX-T Data Center Integration
* Cisco ACI and VMware: The Perfect Pair
* Setting the Record Straight: Confusion about ACI on VMware Technologies