Minecart with Hopper can copy / duplicate items

step 1:crate an ice road to able water transport items
step 2:set a Dropper on the start of the ice road
step 3:set Oak Fence Gate at the end of the ice road where one meter up
step 4:set Rail at the end of the ice road
step 5:put water on the start of the ice road
step 6:set Minecart with Hopper on the rail
step 7:set Button to link the Dropper
step 8:goto the side of the Oak Fence Gate, load the item A to the Dropper and activate the Dropper

result:Item A was copied by Minecart with Hopper.