GWD16-40 请教

Q40:
Which of the following most logically completes the argument?

Researchers recently asked dozens of shoppers, chosen at random coming out of a FoodBasket supermarket, what they had purchased.The prices of the very same items at the nearest ShopperKing supermarket were totaled and compared with the FoodBasket total.The ShopperKing totals averaged five percent higher than the FoodBasket totals.Nevertheless, this result does not necessarily show that shoppers at ShopperKing would save money overall by shopping at FoodBasket instead, since ______.

shoppers who shop regularly at a given supermarket generally choose that store for the low prices offered on the items that they purchase most often
for shoppers with more than 20 items, the ShopperKing totals averaged more than five percent higher than the FoodBasket totals
many shoppers consider factors other than price in choosing the supermarket at which they shop most regularly
there is little variation from month to month in the overall quantity of purchases made at supermarkets by a given shopper
none of the people who conducted the research were employees of the FoodBasket supermarket

这道题答案是A，不明白，我觉得A 的意思是说经常购物的顾客会选择哪些提供日常用品低价格的超市，这表示顾客在F.B.超市购物会省钱啊，好像解释不了结论。