Do you still remember the funny question: why did the chicken cross the road? To get to the other side.    Most people know this joke. But recently, some people have been much more concerned with how the grizzly bear and mountain lion can cross the road.    Millions of animals die each year on US roads, the Federal Highway Administration reports. In fact, only about 80 ocelots , an endangered wild cat exist in the US today. The main reason? Road kill.    "Ecopassages" may help animals cross the road without being hit by cars. They are paths both over and under roads. "These ecopassages can be extremely useful, so that wildlife can avoid human conflicts," said Jodi Hilty of the Wildlife Conservation Society. But do animals actually use the ecopassages? The answer is yes. Paul Beier of Northern Arizona University found foot marks left by mountain lions on an ecopassage that went under a highway. This showed that the lion used the passage.    Builders of some ecopassages try to make them look like a natural part of an area by planting trees on and around them. Animals seem  _ . Animals as different as salamanders  and grizzly bears are using the bridges and underpasses.    The next time you visit a park or drive through an area with a lot of wildlife, look around.  You might see an animal overpass! When the writer says that animals seem "to be catching on", he means   _  .
animals begin to realize the dangers on the road animals are increasing in number animals are crossing the road in groups animals begin to learn to use ecopassages
Question: Do you still remember the funny question: why did the chicken cross the road? To get to the other side.    Most people know this joke. But recently, some people have been much more concerned with how the grizzly bear and mountain lion can cross the road.    Millions of animals die each year on US roads, the Federal Highway Administration reports. In fact, only about 80 ocelots , an endangered wild cat exist in the US today. The main reason? Road kill.    "Ecopassages" may help animals cross the road without being hit by cars. They are paths both over and under roads. "These ecopassages can be extremely useful, so that wildlife can avoid human conflicts," said Jodi Hilty of the Wildlife Conservation Society. But do animals actually use the ecopassages? The answer is yes. Paul Beier of Northern Arizona University found foot marks left by mountain lions on an ecopassage that went under a highway. This showed that the lion used the passage.    Builders of some ecopassages try to make them look like a natural part of an area by planting trees on and around them. Animals seem  _ . Animals as different as salamanders  and grizzly bears are using the bridges and underpasses.    The next time you visit a park or drive through an area with a lot of wildlife, look around.  You might see an animal overpass! When the writer says that animals seem "to be catching on", he means   _  .
A. animals begin to realize the dangers on the road
B. animals are increasing in number
C. animals are crossing the road in groups
D. animals begin to learn to use ecopassages
Answer: