Explanation
When adding the Amazon Web Services (AWS) account to the FortiCNP, you must follow these three mandatory configuration steps:
Add AWS accounts through FortiCNP. This is the first step to enable cloud protection for your AWS account. You can add one or multiple accounts automatically or manually. You need to provide the AWS account ID and a name for the account. You also need to select the optional permissions to be granted to FortiCNP as needed1.
Accept FortiCNP to create CloudTrail for the account. This is required for FortiCNP to collect and analyze the AWS API calls and events. You can choose to let FortiCNP create a CloudTrail for the account or use an existing one. You also need to specify the aggregation region for the CloudTrail1.
Launch the CloudFormation template. This is required for FortiCNP to create a stack and a role in your AWS account. The stack contains the resources that FortiCNP needs to access and monitor your AWS account. The role allows FortiCNP to assume it and perform actions on your behalf. You need to enter a custom or default role name and a unique UUID that is designated for your company on FortiCNP1.
References: Add AWS Account Automatically
https://docs.fortinet.com/document/forticnp/22.4.a/online-help/246021/add-aws-account-automatically

Explanation
The Azure client secret is a one-time value that is only visible when it is created. If the administrator loses or forgets the client secret, they cannot retrieve it from the Azure portal. However, they can create a new client secret and use it to configure Terraform. To create a new client secret, they need to follow these steps12:
Sign in to the Azure portal and navigate to the Azure Active Directory service.
Select the application name under the App Registrations.
Select Certificates & Secrets > New client secret to create a new client secret.
Add a description and an expiration date for the client secret and select Add.
Copy the value of the new client secret immediately as it will not be shown again.
References:
Generate new Client Secret and link to key-vault | Microsoft Learn
Azure Quickstart - Set and retrieve a secret from Key Vault using Azure portal | Microsoft Learn

Explanation
The correct answer is C and D. Use a transit VPC with hub and spoke topology to create multiple VPN connections to the on-premises data center. Use the transit gateway attachment with VPN option to create multiple VPN connections to the on-premises data center.
According to the Fortinet documentation for Public Cloud Security, a transit VPC is a VPC that serves as a global network transit center for connecting multiple VPCs, remote networks, and virtual private networks (VPNs). A transit VPC can use a hub and spoke topology to create multiple VPN connections to the on-premises data center, using the FortiGate VM as a virtual appliance that provides network security and threat prevention.A transit VPC can also leverage Equal-Cost Multi-Path (ECMP) routing to achieve higher bandwidth and load balancing across multiple VPN tunnels1.
A transit gateway is a network transit hub that connects VPCs and on-premises networks. A transit gateway attachment is a resource that connects a VPC or VPN to a transit gateway. You can use the transit gateway attachment with VPN option to create multiple VPN connections to the on-premises data center, using the FortiGate VM as a virtual appliance that provides network security and threat prevention.A transit gateway attachment with VPN option can also leverage ECMP routing to achieve higher bandwidth and load balancing across multiple VPN tunnels2.
The other options are incorrect because:
Using ECMP and VPN to achieve higher bandwidth is not a complete solution, as it does not specify how to replace the existing VPC peering topology or how to connect the AWS VPCs to the on-premises data center.
Using transit VPC to build multiple VPC connections to the on-premises data center is not a correct solution, as it does not specify how to use a hub and spoke topology or how to leverage ECMP routing for higher bandwidth.
1:Fortinet Documentation Library - Transit VPC on AWS2:Fortinet Documentation Library - Deploying FortiGate VMs on AWS

Explanation
The variables.tf file shows that the FortiGate VM will be deployed in the eu-West-Ia region with private and public subnets. The region variable is set to "eu-west-1" and the availability_zone variable is set to
"eu-west-1a". The vpc_id variable is set to "vpc-0e9d6a6f" and the subnets variable is set to a list of two subnet IDs: "subnet-0f9d6a6f" and "subnet-1f9d6a6f". The license_type variable is set to "on-demand" and the ami_id variable is set to "ami-0e9d6a6f".
References:
https://docs.fortinet.com/document/fortigate/6.4.0/aws-cookbook/236478/deploying-fortigate-vm-on-aws-using-t

Explanation
A VPC attachment is the type of attachment that allows you to connect a VPC to a TGW and advertise routes through BGP. A VPC attachment creates a VPN connection between the VPC and the TGW, and enables dynamic routing with BGP. A connect attachment is used to connect a VPN or Direct Connect gateway to a TGW. A route attachment is not a valid type of attachment for TGW. A GRE attachment is used to connect a FortiGate device to a TGW using GRE tunnels. References:
Creating the TGW and related resources
Configuring TGW route tables
FortiGate Public Cloud 7.2.0 - Fortinet Documentation
Updating the route table and adding an IAM policy