The exhibit shows the FortiGuard category-based filter has "File Sharing and Storage" set to "Block." Since www.dropbox.com is categorized under this category, FortiGate will block the connection based on the category filter configuration. This is the standard behavior when category-based filtering is enabled and a specific category is set to block.

A. FortiGate won't block it as "invalid URL" - it's a valid URL in a blocked category.

B. The URL Filter section doesn't show any allow rules for this specific URL.

D. Web Content Filter being enabled doesn't exempt URLs from category-based blocking.

- FortiGate Administration Guide 7.6.0, "Web Filter" chapter, section on "FortiGuard Category Filter"

- FortiGate Security 7.6 Study Guide, "Content Inspection" module, pages on category-based filtering

- Fortinet Document Library, "Web Filtering Best Practices Guide v7.6"