D. SELECT prod_name
FROM products
WHERE (unit_price *qty_in_hand) = (SELECT MAX(SUM(unit_price * qty_in_hand))
FROM products)
GROUP BY prod_name;
Answer: A
解析：
(SELECT MAX(unit_price* qty_in_hand) FROM products) 得到unit_price *qty_in_hand的最大值
SELECT prod_name
FROM products
WHERE (unit_price* qty_in_hand) = (SELECT MAX(unit_price * qty_in_hand)
FROM products);
(unit_price *qty_in_hand) =最大值 所以能得到正确的结果