A data engineer is tasked with converting the quantity of food grains from kilograms to tons for a client dealing in agricultural products. The quantities are stored in a table named food_items. Given the schema of this table, which higher-order function should be used in the following query to achieve the desired conversion? (Note: 1 ton = 1000 kg)

SELECT warehouse_id,
food_grains,
____________ as food_grains_qty_in_tons
FROM food_items;