Transparent mode allows the FTD device to act as a "bump in the wire" that does not affect the IP addressing of the network. The end user workstations will not need any changes to their configuration, as they will still receive an IP address from the same DHCP server. However, the FTD device must allow DHCP traffic in the access control policies, otherwise it will block the DHCP requests and replies1

If an engineer receives a 403: Forbidden error when attempting to download a packet capture file from Cisco Secure Firewall Management Center (FMC), the issue is likely due to HTTPS not being enabled in the device platform policy. To resolve this issue, the engineer must enable HTTPS in the platform policy.
Steps:
* In FMC, navigate to Policies > Device Management > Platform Settings.
* Edit the relevant platform policy.
* Enable HTTPS for the device.
* Deploy the changes to the FTD device.
This ensures that the FMC and FTD device can securely transfer the packet capture file over HTTPS, resolving the 403 error.
References: Cisco Secure Firewall Management Center Administrator Guide, Chapter on Platform Settings and HTTPS Configuration.

To configure URL filtering for a Cisco FTD device in Cisco FMC, and to meet the requirements of the question, the engineer must do the following:
On the HTTP Responses tab of the access control policy editor, set the Interactive Block Response Page to system-provided. This will enable the system to display a warning page to the users when they try to access a blocked URL, and give them the option to continue or cancel. The system-provided page is a default page that contains a generic message and a logo1.
Configure
an access control rule that matches an URL object for http://www.badadultsite.com; and set the action to Interactive Block. This will apply the interactive block action to the specific URL that is defined in the URL object. The interactive block action will trigger the interactive block response page that was configured in the previous step1.
The other options are incorrect because:
On the HTTP Responses tab of the access control policy editor, setting the Block Response Page to Custom will not affect the interactive block action. The block response page is used when the action is set to Block, not Interactive Block1.
Configuring the default action for the access control policy to Interactive Block will apply the interactive block action to all URLs that are not matched by any access control rule. This will not meet the requirement of blocking no other websites1.
Configuring
an access control rule that matches the Adult URL category and sets the action to Interactive Block will apply the interactive block action to all URLs that belong to the Adult category. This will not meet the requirement of blocking only http://www.badadultsite.com1.