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