There were signs here and there,_____visitors to look out for
There were signs here and there,_____visitors to look out for ____rocks.
A warning,fallen
B warning,falling
c warned,falling
d to warm,fallen
参考答案:答案是 B warning,falling
warning短语直到句末，是现在分词短语作定语，其解释说明作用。falling是现在分词，意思是“正在落下的”，作rocks的定语。