To troubleshoot an issue with the Phase 1 proposal from an Azure Virtual Network gateway when connecting to a site-to-site VPN connection by reviewing logs, you should analyze the IKE Diagnostic log. Therefore, option C is correct. You should analyze the IKE Diagnostic log.

According to the given scenario, the application deployed on four Standard_D2_v3 virtual machines behind an Azure Load Balancer is experiencing slow performance during peak usage periods It is reported that the peak usage for each VM is approximately 1 Gbps, and the goal is to increase the throughput to a minimum of 10 Gbps.
To achieve this goal, the best option is to increase the size of the VM instance. The Standard_D2_v3 virtual machine size has a maximum network bandwidth of 1 Gbps, so increasing the size of the VM instance to a higher tier, such as Standard_D8_v3 or higher, will provide more network bandwidth and improve the application's performance.
Option A, requesting an increase in networking quotas, may not be sufficient to achieve the required network bandwidth.
Option C, disabling the Azure Firewall and implementing network security groups, may not have a significant impact on the network bandwidth.
Option D, moving two of the servers behind a separate load balancer and configuring round-robin routing in Traffic Manager, may improve availability and performance but will not increase the network bandwidth.
Source: [1] https://docs.microsoft.com/en-us/azure/virtual-machines/windows/sizes-general [2] https://docs.microsoft.com/en-us/azure/virtual-network/designing-hub-spoke-topologies#optimize-data-transfer-between-hub-and-spoke-vnets

Azure Site Recovery supports replicating VMware VMs that meet certain requirements for operating system version, disk type and size, network adapter type and configuration, and so on. Based on the table of VMs and their properties, only VM1 meets all the requirements for replication

According to Microsoft, the ICMP protocol is not permitted through the Azure load balancer. To test connectivity, Microsoft recommends that you do a port ping. While Ping.exe uses ICMP, you can use other tools, such as PSPing, Nmap, and telnet, to test connectivity to a specific TCP port1.

Azure Site Recovery has limits on data change rates depending on the type of disk used for replication. If a VM has a data change rate higher than the supported limit for its disk type, it can cause replication issues or errors. To resolve this issue, you can upgrade the target storage disk to a higher tier that supports higher data change rates.