Which words in the passage show that the passage has a Problem and Solution Structure?
In most parts of the world there are not as many crocodiles as there used to be. This is a problem because crocodiles are becoming endangered and also crocodiles are necessary to the balance of nature. Many crocodiles have died because people dried up the swamps and marshes where the crocodiles live. Poachers have also contributed to the dilemma as crocodiles have been desired for their strong, smooth, leathery skins. In order to preserve these mighty creatures, people must take care of the crocodiles’ environment and help put a stop to the needless shooting of these animals.
A. This is a problem
B. crocodile are necessary to the balance of nature.
C. crocodiles have been desired for their strong, smooth, leathery skins.

As the name suggests, a problem and solution structure is used to present a problem, issue, or even a dilemma and then the possible solutions that can be or have already been attempted. Some authors will describe the problem without actually using the word "problem". Others will choose to make it as clear and direct as possible, which is the case here. The author of the excerpt wants to make it crystal clear that the killing of crocodiles is an issue that needs to be addressed, so he uses the words "this is a problem". He then explains why that is a problem and, even though we only have a passage here, we can safely assume he will offer option for solutions.