Concept:Important documents need extra security and proof of handling.
Registered mail provides the highest safety among postal services.
Explanation:Registered mail is a special postal service that handles letters and parcels with extra care.
It gives a receipt at the time of posting and keeps a detailed record of the item's movement.
The item is kept under lock and key and is signed for at every stage of transit.
Delivery is made only to the addressee or an authorised person.
If the item is lost or damaged, the sender can claim compensation from the postal department.
Other options such as parcel post, letter post, or express mail do not offer the same level of security and compensation.
Therefore, for sending important documents, registered mail is the safest choice.
Answer:A. Registered mail