According to the FortiOS 7.6 AWS Administration Guide and the Fortinet Public Cloud Security 7.4 training materials regarding centralized security inspection:

Multiple Route Tables (Option B): A single AWS Transit Gateway is designed to support multiple TGW route tables. By default, there is a soft limit of 20 route tables per Transit Gateway, which allows administrators to implement sophisticated network segmentation and granular routing policies. In a FortiGate-centric "Security Hub" or "Transit VPC" architecture, multiple route tables are used to separate "Spoke" traffic from "Security" traffic, ensuring all inter-VPC traffic is forced through the FortiGate-VM for inspection.

Associations and Propagations: * Association: Each individual TGW attachment (VPC, VPN, or Direct Connect) can be associated with exactly one TGW route table at any given time. This table dictates where packets coming from that attachment will be sent. Because of this 1:1 relationship, Option C is incorrect.

Propagation: An attachment can propagate its routes to one or many TGW route tables. This flexibility allows a VPC's prefix to be known in multiple routing domains, meaning that association and propagation do not need to occur in the same table, making Option A incorrect.

Default Route Table Management: When creating an AWS Transit Gateway, the options for "Default route table association" and "Default route table propagation" are enabled by default, but they can be disabled during or after creation. Disabling these is a security best practice when deploying FortiGate-VMs to prevent the TGW from automatically creating a "full-mesh" connectivity that bypasses the firewall, making Option D incorrect.

The Fortinet documentation states: "An IGW in AWS is a VPC component that allows communication between instances in your VPC and the internet... AWS users with less experience may face connectivity issues if they create a new VPC, add EC2 instances to it, but forget that they need an IGW for internet connectivity."

Based on the Fortinet NSE 7 - Public Cloud Security 7.4/7.6 curriculum and Azure Resource Manager (ARM) deployment logic, the what-if tool provides a predictive analysis of infrastructure changes.

Analyzing the Modification Symbols (Option B): The exhibit shows several critical changes being attempted simultaneously on the ServerApps_vnet.

VNet Address Space Change: The symbol - (Delete) is next to the address space 10.0.0.0/16, and + (Create) is next to 192.168.0.0/24.

Subnet Modification: Further down, the symbol ~ (Modify) indicates an attempt to change the prefix of an existing subnet from 10.0.1.0/24 to 10.0.2.0/24.

Azure Deployment Constraints: According to the FortiOS 7.6 Azure Administration Guide, Azure networking has strict dependencies. You cannot delete or modify an address space that contains active subnets or resources.

Why the deployment fails: The what-if output shows the administrator is trying to remove the 10.0.0.0/16 address range. However, the existing subnet 10.0.1.0/24 is still "resident" within that range during the transaction. Because the subnet is currently attached to the address space being deleted, Azure Resource Manager will reject the deployment as an invalid operation. The attempt to add a new 192.168.0.0/24 range does not resolve the conflict of removing the active range.

Why other options are incorrect:

Option A: The tool shows that 10.0.1.0/24 is being changed to 10.0.2.0/24, not that one is replacing the other as a new entity.

Option C: The symbols show a modification (~) of an existing subnet (index 0:), not the creation (+) of an entirely new subnet.

Option D: The VNet name ServerApps_vnet is not being changed; only its internal properties (tags, address space, and subnets) are being modified.