Concept:Registered mail provides the highest level of security and proof of delivery for postal items.
Explanation:The key requirement is that the item is delivered to the named address and not just handed to anyone.
Registered mail gives the sender a receipt at the point of posting.
The item is then tracked throughout its journey.
Most importantly, the receiver must sign to confirm receipt at the correct address.
This signature creates a clear record proving the named recipient actually received the item.
Other options are less reliable: recorded delivery may not have full tracking, certificate of posting only proves posting, and express mail only focuses on speed.
Therefore, registered mail is the most secure way to ensure delivery to the named addresses.
Answer:C. Registered mail