Step 1: A digger is the standard machine used to lift potatoes out of the soil, exposing the tubers so they can be picked up. So (A) Digger pairs with (II) Potato.
Step 2: A reaper is built to cut standing cereal crops like wheat and paddy at their base, so (B) Reaper pairs with (III) Cereal crops.
Step 3: A picker, specifically a cotton picker, is designed to pull cotton lint out of the open bolls on the plant, so (C) Picker pairs with (I) Cotton.
Step 4: A snapper is a machine built to snap corn ears off the maize stalk without husking them, so (D) Snapper pairs with (V) Maize.
Step 5: A mower cuts and lays down forage and grass crops for hay or silage, so (E) Mower pairs with (IV) Forage crops.
Step 6: Putting these together gives (A)-(II), (B)-(III), (C)-(I), (D)-(V), (E)-(IV), matching option 4.