That 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 departments.
Which of the following, if true, most strengthens the argument
A．On particularly cloudy days, more artificial light is used to illuminate the part of the store under the skylight.
B．When the store is open at night, the departments in the part of the store under the skylight have sales that are no higher than those of other departments.
C．Many customers purchase items from departments in both parts of the store on a single shopping trip.
D．Besides the skylight, there are several significant architectural differences between the two parts of the store.
E．(E) The departments 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.