The sales can be increased by the presence of sunlight within a store has been shown by the experience of the only Savefast department store with a large skylight. The skylight allows sunlight into half of the store, reducing the need for artificial light. The rest of the store uses only artificial light. Since the store opened two years ago, the departments on the sunlit side have had substantially higher sales than the other departmens.

Which of the following, if true, most strengthens the argument?

  答案是When the store is open at night, the department in the part of the store under the skylight have sales that are no higher than those of other department.

它还有一个选项是The department in the part of the store under the skylight are the departments that generally have the highest sales in other stores in the Savefast chain.这个为什么不可以呢？