American lunch hour is usually from noon until one o'clock or from one until two. People at work or school rarely go home for lunch. Instead, many bring lunch with them from home. For this purpose they need a meal that is small, portable, and does not require constant refrigeration. The sandwich meets all these three requirements.

When it comes to talking about the sandwich, Americans can offer you a long list of its names: a submarine sandwich, a hero, a hoagie, a grinder, a pool boy, a torpedo, a club sandwich and an open sandwich. Whatever you call it, this concoction (混合) of cold cuts in a roll is as American as the hot dog or the apple pie. In attempting to track down its origin, it is found that several U.S. cities claim to be its birthplace—New Orleans, New York, Philadelphia, and Chester. A strong possibility is the simultaneous, independent invention of all these cities. Whatever it started, the sandwich was clearly an innovation of the Italian immigrants, In their old country, Italian workers had gone home at midday for their lunch; since U.S. factory owners frowned on this practice, they adopted the roll as a kind of lunchbox and put their meat and cheese within. In this way, an inexpensive yet filling meal could be carried to the workplace without damage. Hence we can see the sandwich as a compromise between the Old World attachment to sausages and cheese, and the need in the American workday context.

The sandwich remained largely a working-class item from its beginning in the 1580s. Then during the Depression the financially suffered middle class realized its value as an economical meal and transformed it into an American staple （生活必需品）.
The most important feature of the sandwich as lunch is ________.（　）

A.nutritious

B.economical

C.portable

D.free from disease germs