There were signs here and there, visitors to look out for rocks.
A. warning; fallen
B. warned; falling
C. to warn; fallen
D. warning; falling
网友回答
A. warning; fallen
B. warned; falling
C. to warn; fallen
(答案→)D. warning; falling
解析：考查非谓语动词用法。第一空的warn与sign构成主动关系，所以使用现在分词的形式。第二空是分词做定语,falling修饰rocks.句意：到处都有些标牌，警告游客当心下落的岩石。