单项选择题

TEXT B
The tradition of christening and commissioning a ship dates back to ancient times when the Greeks, Romans, Egyptians and Vikings called upon the gods to protect their ships and crew from the perilous sea. Religion played an important role in these ceremonies. In fact, christenings originated as a way to appease the gods of the elements. Christening gave a ship its identity, and over the years, different cultures and people changed and shaped the way ceremonies were performed.
Some of these traditions have been carried over into modem times. A ship is traditionally christened or given its name at the time it is launched into the water. When a ship is christened, it is a tradition to break a bottle across the ship’s bowl. This practice began in Britain in the late seventeenth century. Previously, an official would sip wine from a "standing cup," a large loving cup made of precious metal, then pour out the remaining wine onto the deck or over the ship’s bow. The cup was then tossed overboard. This practice soon became too costly and a net was used to catch the cup so it could be re-used at other launchings. Wine was the traditional liquid used to christen a ship, although other liquids were used such as whiskey, brandy and water. At the close of the nineteenth century champagne became the popular liquid with which to christen a ship. However, during prohibition in America, ships were christened with water.
Ships’ sponsors were generally royalty or senior naval officers. In the nineteenth century, women became ship sponsors for the first time. Women sponsored ships more and more frequently, although it was not the rule. The actual physical process of launching a new ship from a building site to the water involved one of three principal methods. Oldest, most familiar and most widely used, was the "end-on" launch in which the vessel slid, usually stern first, down an inclined slipway. The "side launch," whereby the ship entered the water broadside, came into nineteenth-century use on inland waters, rivers and lakes. It was given major impetus in America by the World War II building program. Another method involved ships built in basins or graving docks, which were floated by admitting water into the dock. The commissioning ceremony then completed the cycle from christening and launching, to full status for active service.
According to the passage, one practice became too costly because ______.