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The first navigational lights in the New World were probably lanterns hung at harbor entrances. The first lighthouse was put up by the Massachusetts Bay Colony in 1716 on Little Brewster Island at the entrance to Boston Harbor. Paid for and maintained by "light dues" levied (征收) on ships, the original beacon was blown up in 1776. Until then there were only a dozen or so true lighthouse in the colonies. Little over a century later, there were 700 lighthouses.
The first eight lanterns erected on the West Coast in the 1850’s featured the same basic New England design: a Cape Cod dwelling with the tower rising from the center or standing close by. In New England and elsewhere, though, lighthouses reflected a variety of architectural styles. Since most stations in the Northeast were set up on rocky eminences (高处), enormous towers were not the rule.
　　Some of them were made of stone and brick, others of wood or metal. Some of them stood on pilings or sti
A. The training of the lighthouse keepers.
B. The sturdiness of the lighthouses.
C. The visibility of the lights.
D. The locations of the lighthouses.